bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanism of growth delay induced in Escherichia coli by near ultraviolet radiation.
Authors: Ramabhadran T V , Jagger J
Published: May 2006

Continuously growing cultures of E. coli B/r were irradiated with a fluence of broad-band near-ultraviolet radiation (315-405 nm) sufficient to cause extensive growth delay and complete cessation of net RNA synthesis. Chloramphenicol treatment was found to stimulate resumption of RNA synthesis, similar to that observed with chloramphenicol treatment after amino-acid starvation. E. coli strains in which amino-acid starvation does not result in cessation of RNA synthesis ("relaxed" or rel- strains) show no cessation of growth and only a slight effect on the rate of growth or of RNA synthesis. These findings show that such near-UV fluences do not inactivate the RNA synthetic machinery but affect the regulation of RNA synthesis, in a manner similat to that produced by amino-acid starvation. Such regulation is believed to be mediated through alterations in concentration of guanosine tetraphosphate (ppGpp), and our estimations of ppGpp after near-UV irradiation are consistent with such an interpretation. These data, combined with earlier published data, strongly suggest that the mechanism of near-UV-induced growth delay in E. coli involves partial inactivation of certain tRNA species, which is interpreted by the cell in a manner similar to that of amino-acid starvation, causing a rise in ppGpp levels, a shut-off of net RNA synthesis, and the induction of a growth delay.
Thyroid hormone stimulates de novo growth hormone synthesis in cultured GH1 cells: evidence for the accumulation of a rate limiting RNA species in the induction process.
Authors: Samuels H H , Shapiro L E
Published: May 2006

We have previously demonstrated with radioimmunoassay techniques that physiologic concentrations of thyroid hormone stimulate an increase in growth hormone production in GH1 cells in culture. In this study, with radiolabel techniques and selective immunoprecipitation, we demonstrate that L-triiodothyronine stimulates growth hormonw production solely by inducing an increase in the de novo synthesis of the polypeptide hormone. L-Triiodothyronine stimulated synthetic rates of growth hormone by 1.5-fold in 1.25 hr, 2-fold in 2.5 hr, to a maximal of 3- to 4-fold after 8.5 hr of incubation. The time interval between significant L-triiodothyronine binding to putative nuclear receptors and a detectable increase in growth hormone synthesis was 45-60 min. Studies on the effect of actinomycin D, 3'-deoxyadenosine, and cycloheximide support the thesis that L-triiodothyronine induces the accumulation of an RNA species which is rate limiting for growth hormone synthesis and lends further support for a primary action of thyroid hormone at the nuclear level.
Deficiency in plasma protein synthesis caused by x-ray-incuded lethal albino alleles in mouse.
Authors: Garland R C , Satrustegui J , Gluecksohn-Waelsch S , Cori C F
Published: May 2006

Plasma protein synthesis was studied in mice bearing x-ray induced lethal mutations at the albino locus. Newborn albino mutants showed a decrease in each of the three principal plasma proteins, albumin, alpha-fetoprotein, and transferrin, when compared with colored littermate controls. Incorporation of [14C]leucine into plasma proteins of the newborn albinos 30 min after injection was only 1/5 that of the controls, but incorporation into total liver protein was only slightly diminished. Incorporation of [14C]leucine into an albumin fraction obtained by immunoprecipitation from livers incubated in vitro in an amino acid mixture was also strongly diminished. Thus, the liver of 18-day-old albino fetuses incorporated into this fraction 1/3 and that of newborn albinos 1/8 as much as the controls, but in both cases the incorporation into total liver protein was only 25% less than in the respective controls. These results indicate that the rather severe structural abnormalities observed in the mutants in the endoplasmic reticulum and the Golgi apparatus are not associated with a general deficiency of hepatic protein synthesis. Instead the data from this and previous work show that the progressive deficiency from fetal life to birth involves certain specific proteins represented by several perinatally developing enzymes and by plasma proteins. It is suggested that the mutational effects observed in these mice are due to deletions involving regulatory rather than structural genes at or near the albino locus.
A possible explanation for the nuclease limit digestion pattern of chromatin.
Authors: Cantor C R
Published: May 2006

The general pattern of DNA fragments in the limit digest of nuclease-treated chromatin could arise from a single, unique nuclease-susceptible site per nucleosome. If DNA binds to the histone core of the nucleosome along a circularly re-entrant path, the location of the DNA entrance and exit can occur at any of a number of distinct sites. This very specific type of heterogeneity together with the natural 10-fold periodicity of DNA B can account for the observed digestion pattern. Such a general picture of the nucleosome structure could also easily explain how nucleosomes might move along the DNA. This type of structure should be easy to distinguish experimentally form more conventional explanations of the origin of the limit digest pattern of chromatin.
Insulin release and phosphate ion efflux from rat pancreatic islets induced by L-leucine and its nonmetabolizable analogue, 2-aminobicyclo[2.2.1]heptane-2-carboxylic acid.
Authors: Freinkel N , Younsi C E , Dawson R M
Published: May 2006

When isolated rat pancreatic islets that had been labeled with 32P were exposed to 10mM L-leucine in a microperifusion system, there was a transitory, immediate heightened efflux of [32P]phosphate ions. Commencement of the phosphate flush coincided with the first release of insulin, and it occurred in the absence or presence of nonstimulatory levels of glucose (0.5 mg/ml). The effects of leucine upon phosphate efflux were not inhibited by D-mannoheptulose, whereas glucose-induced stimulations were suppressed. The phosphate flush could be induced also by the nonmetabolizable analogue of leucine, 2-aminobicyclo[2.2.1]heptane-2-carboxylic acid. Like insulin release, the effect was stereospecific, with only one of the four stereoisomers, (-)-b-aminobicycloheptane carboxylic acid, being active. Analogue-induced phosphate and insulin release were totally suppressed in a medium containing D2O, but on reversion to H2O the efflux of both hormone and anion occured. It is concluded that insulin secretion from islet beta cells and the release of phosphate ions showed the same specificity for nutrient secretagogues and that both can be triggered even in the absence of exogenous oxidizable fuels. However, the partial dissociation of the dose-response curves for the two phenomena lends support to the contention that the phosphate flush reflects an earlier event in the sequence of stimulus-secretion coupling.
Amino-acid sequence of equine renal metallothionein-1B.
Authors: Kojima Y , Berger C , Vallee B L , Kägi J H
Published: May 2006

The amino-acid sequence of a metallothionein is reported. Metallothionein is a widely distributed, extremely cysteine-rich, low-molecular-weight protein containing large amounts of cadmium and/or zinc. Metallothionein-1B is one of the two prinicipal variants occurring in equine kidney cortex. The single-chain protein contains 61 amino acids and has the composition Cys20 Ser8Lys7Arg1Ala7Gly5Val3Asp2Asn1-Glu1Gln2Pro2Thr1Met1(Cd + Zn)7. Its amino-terminal residue is N-acetylmethionine. The sequence shows distinct clustering of the twenty cysteinyl residues into seven groups separated by stretches of at least three other residues. Within these groups the cysteines occur seven times in alternating Cys-X-Cys sequences and three times each in Cys-Cys and Cys-X-X-Cys sequences, where X is an amino acid other than cysteine. Another unique feature is the close association of serine and the basic amino acids with cysteine, as manifested by the occurrence of seven Ser-Cys, four Cys-Lys, one Cys-Arg, and three Lys-Cys sequences. These findings are in agreement with the previous suggestion that metallothionein has structurally defined metal-binding sites, most of which contain three cysteinyl residues as the principal metal-binding ligands. The charge difference between the metal-free and the metal-containing protein is consistent with the formation of negatively charged trimercaptide complexes with cadmium and/or zinc ions. The possible additional involvement of serine and the basic amino acids in metal binding is discussed.
Nature of conformational changes in poly[d(A-T)-d(A-T)] in the premelting region.
Authors: Brahms S , Brahms J , Van Holde K E
Published: May 2006

The conformation of the synthetic DNA, poly-[d(A-T)-d(A-T)], has been investigated both in the solid state and in dilute aqueous solutions at different temperatures below its melting point. The change of the circular dichroism (CD) spectra of poly[d(A-T)-d(A-T)] solutions with decreasing temperatures from just below the melting point to 0 degrees involves a specific decrease of the intensity of the 262 nm CD band. This conformational change has been assigned to a gradual and partial transition from the B to C form, on the basis of the following results: (i) By the use of infrared dichroism measurements on oriented films we have defined humidity and salt conditions under which B and C forms of poly[d(A-T)-d(A-T](Li+) are stable. In addition, we find that ammonium salts induce the C form of poly[d(A-T)-d(A-T)] even at high relative humidity. (ii) CD studies of the films of the lithium salt of poly[d(A-T)-d(A-T)] under the same conditions have given CD spectra corresponding to the B and C forms of this polynucleotide. In addition, the CD spectrum of the ammonium salt of poly[d(A-T)-d(A-T)] in solution approaches that of the C form in films. (iii) The conformational change of poly[d(A-T)-d(A-T)] as a function of temperature can be entirely explained on the basis of changes in the double-stranded base-paired structure. Our data rule out hydrogen bond breaking and unstacking or "breathing" as an explanation of the premelting changes. Curves of the continuous variation of CD(epsilon at 262 nm) as a function of temperature (from 0 degrees to the melting zone) show similar slopes in the presence of different agents stabilizing the double-stranded structure, such as Mg++, or at different salt concentration (KCl), indicating that the nature of the process is independent of ionic strength. Some specific effects were observed in the influence of certain neutral salts; ammonium induces the C form whereas magnesium favors the B form. CD data give direct evidence that a DNA like poly[d(A-T)-d(A-T)] need not change conformation upon transition from a dilute aqueous solution to a highly hydrated (film/gel) solid state. The change of conformation begins only at a defined partial dehydration.
In vitro replication of simian virus 40 DNA in a nucleoprotein complex.
Authors: Su R T , DePamphilis M L
Published: May 2006

A simian virus 40 (SV40) nucleoprotein complex, extracted from nuclei isolated from a monkey cell line infected with SV40, continued DNA replication in the presence of a nuclear extract, cytosol, ATP, and ATP-regenerating system, and the four deoxyribonucleoside triphosphates. The DNA products of replication were also found as nucleoprotein complexes. Forty percent of the replicating viral DNA, labeled in vivo, was converted into covalently closed, superhelical DNA during incubation in vitro. Although the remaining labeled DNA was not converted into mature viral DNA, it was elongated to its full genome length. Failure to terminate replication successfully was not caused by endonuclease activity, since covalently closed DNA, labeled in vivo, was not damaged during incubation in vitro. When [alpha-32P]dATP was present during the incubation, the label appeared first in replicating DNA and later in mature DNA; no unusual products were labeled in vitro. The covalently closed SV40 DNA made in vitro had the same superhelical density as viral DNA made in vivo. These data demonstrate that viral nucleoprotein complexes ("minichromosomes") are able to continue DNA replication outside of the nucleus.
Mechanism of DNA elongation catalyzed by Escherichia coli DNA polymerase III, dnaZ protein, and DNA elongation factors I and III.
Authors: Wickner S
Published: May 2006

Elongation of a primed single-stranded DNA template catalyzed by E. coli DNA polymerase III (DNA nucleotidyltransferase, deoxynucleosidetriphosphate:DNA deoxynucleotidyltransferase, EC 2.7.7.7) requires dnaZ protein and two other protein factors, DNA elongation factors I and III. The reaction occurs by the following mechanism: (i) dnaZ protein and DNA elongation factor III together catalyze the transfer of DNA elongation factor I to a primed DNA template. This transfer reaction requires ATP or dATP in addition to dnaZ protein, DNA elongation factors I and III, and primed template; it does not require DNA polymerase III. (ii) DNA polymerase III binds to the complex of DNA elongation factor I with primed template; it does not bind to primed template which is not complexed with DNA elongation factor I. This binding reaction proceeds in the absence of ATP or dATP as cofactor, dnaZ protein, and DNA elongation factor III and without additional DNA elongation factor I. (iii) The complex of DNA polymerase III, DNA elongation factor I, and primed template catalyzes DNA synthesis upon the addition of dNTPs.
Trimodality in the proportion of hemoglobin G Philadelphia in heterozygotes: evidence for heterogeneity in the number of human alpha chain loci.
Authors: Baine R M , Rucknagel D L , Dublin P A , Adams J G
Published: May 2006

The extent of variability in the number of human hemoglobin (Hb) alpha chain loci has not yet been conclusively determined. There is evidence that in some populations individuals may possess two alpha-chain loci, while in other populations only one locus is present. Electrophoresis of peripheral blood from 53 heterozygotes for Hb G Philadelphia (alpha 68 Asn leads to Lys) revealed that the proportion of Hb G is trimodally distributed, with modes at approximately 20, 30, and 40% Hb G. Familial, hematologic, and statistical studies suggest that hte proportion of Hb G is not random but is genetically controlled and inversely correlated with mean cell volume. Two alternative genetic models are proposed to explain these findings: one assums alpha-thalassemia, while the other postulates variability in the number of alpha-chain loci in the American Black population. Biosynthetic studies of blood from 15 subjects revealed balanced synthesis of alpha and beta globin chains in heterozygotes from all three classes, strongly supporting variable gene dosage rather than alpha-thalassemia as the mechanism underlying the observed trimodality in the proportion of Hb G. Incompatibilities between out results and current concepts of alpha-thalassemia are discussed in the context of differences between Black compared with Oriental and Italian forms of Hb H disease.
Sex ratio, sex change, and natural selection.
Authors: Leigh E G , Charnov E L , Warner R R
Published: May 2006

We describe the analogy between the theory of natural selection on sex ratio in newborn gonochores (which will not change sex), and on the age of sex change in sequential hermaphrodites (which are all born into one sex and change to the other later on). We also discuss the conditions under which natural selection favors sequential hermaphrodites over gonochores and vice versa. We show that, in a nearly stable population of nearly constant age composition, selection favors a rare mutant if it increases the prospective reproduction of its newborn bearers that are (or while they are) members of one sex by a percentage exceeding the percentage loss to the other sex.
Structural studies on protein products of murine chromosome 17: partial amino acid sequence of an H-2Kb molecule.
Authors: Capra J D , Vitetta E S , Klapper D G , Uhr J W , Klein J
Published: May 2006

By use of single internal radiolabels, 17 of the NH2-terminal 27 amino acids of the murine H-2Kb molecule have been assigned. When the amino acid sequence is compared to that of the murine H-2Kk molecule, there is a minimum of six amino acid differences in 19 positions. This high degree of structural diversity confirms, at the level of amino acid sequence, the known polymorphism of the murine H-2 complex. Significant primary str-ctural homology is evident when the murine H-2Kk and H-2Kb sequences are compared to the recently reported partial amino acid sequences of human transplantation antigens. There is modest homology with beta2-mictoglobulin and immunoglobulins, but the available sequence information is insufficient for a satisfactory evaluation of its significance.
Supplemental ascorbate in the supportive treatment of cancer: Prolongation of survival times in terminal human cancer.
Authors: Cameron E , Pauling L
Published: May 2006

Ascorbic acid metabolism is associated with a number of mechanisms known to be involved in host resistance to malignant disease. Cancer patients are significantly depleted of ascorbic acid, and in our opinion this demonstrable biochemical characteristic indicates a substantially increased requirement and utilization of this substance to potentiate these various host resistance factors. The results of a clinical trial are presented in which 100 terminal cancer patients were given supplemental ascorbate as part of their routine management. Their progress is compared to that of 1000 similar patients treated identically, but who received no supplemental ascorbate. The mean survival time is more than 4.2 times as great for the ascorbate subjects (more than 210 days) as for the controls (50 days). Analysis of the survival-time curves indicates that deaths occur for about 90% of the ascorbate-treated patients at one-third the rate for the controls and that the other 10% have a much greater survival time, averaging more than 20 times that for the controls. The results clearly indicate that this simple and safe form of medication is of definite value in the treatment of patients with acvanced cancer.
An oscillatory neuronal circuit generating a locomotory rhythm.
Authors: Friesen, W O , Poon M , Stent G S
Published: May 2006

A quartet of interconnected interneurons whose periodic activity appears to generate the traveling body wave of the swimming leech has been identified on each side of segmental ganglia of the ventral nerve cord of Hirudo medicinalis. Theoretical analysis and electronic analog models of the identified intra- and interganglionic synaptic connections of the segmentally iterated interneurons showed that they form an oscillatory network with cycle period and intra-and intersegmental phase relations appropriate for the swimming movement.
Subcellular localization of S-adenosyl-L-methionine:tRNA methyltransferases with aminoacyl-tRNA synthetases in human and mouse: normal and leukemic leukocytes.
Authors: Agris P F , Woolverton D K , Setzer D
Published: May 2006

The subcellular distributions of S-adenosyl-L-methionine:tRNA methyltransferases and aminoacyl-tRNA synthetases were investigated with the use of human and mouse normal and leukemic leukocyte cell lines. Differential centrifugation of homogenized cell suspensions produced three pelleted subcellular fractions (nuclear and membrane, microsomal, and postribosomal) and a supernatant fraction. Each fraction was assayed for both methyltransferase activity and synthetase activity. The largest amounts, 40-50%, of total methyltransferase and synthetase activities were localized in either the microsomal or the postribosomal fractions, depending on cell type. In addition, the highest specific activities of these two enzyme systems were found to be present in the microsomal and postribosomal fractions. The psotribosomal fraction from leukemic leukocytes had a methyltransferase specific activity higher than that of the microsomal fraction, while the same two fractions of normal leukocytes had approximately equal activities. Specific activities of aminoacyl-tRNA synthetases were found to be approximately equal for these two fractions, whether they were from normal or leukemic leukocytes. The activity of tRNA methyltransferases and synthetases within the postribosomal fraction of the cytoplasm suggests the existence of high-molecular-weight enzyme complexes for the modification as well as the aminoacylation of tRNA.
Isolation, primary structure, and synthesis of α-endorphin and γ-endorphin, two peptides of hypothalamic-hypophysial origin with morphinomimetic activity
Authors: Ling Nicholas , Burgus Roger , Guillemin Roger
Published: May 2006

The isolation and primary structure of two peptides with morphinomimetic activity, obtained from an extract of porcine hypothalamus-neurohypophysis, are described. The amino acid sequence of the two peptides, named α-endorphin and γ-endorphin, was determined by mass spectrometry and densyl-Edman methods to be H-Tyr-Gly-Gly-Phe-Met-Thr-Ser-Glu-Lys-Ser-Gln-Thr-Pro-Leu-Val-Thr-OH and H-Tyr-Gly-Gly-Phe-Met-Thr-Ser-Glu-Lys-Ser-Gln-Thr-Pro-Leu-Val-Thr-Leu-OH, respectively. These correspond to the amino acid sequences present between residues 61 and 76 and residues 61 and 77 of the various β-lipotropins. A third peptide also obtained in pure from in these studies was found to be an unstable salt of α-endorphin.
Colicin E2 is DNA endonuclease.
Authors: Schaller K , Nomura M
Published: May 2006

Colicin E2 purified by conventional methods contains a tightly bound low-molecular-weight protein, as has been found with purified colicin E3 [Jakes,N.&Zinder,N.D.(1974) Proc. Natl. Acad. Sci. USA 71, 3380-3384]. Such E2 preparations do not cause DNA cleavage in vitro. After separation from the low-molecular-weight protein, colicin E2 retained the original in vivo killing activity, and in addition showed a high activity in vitro in cleaving various DNA molecules, such as a ColE1 hybrid plasmid and DNAs from Escherichia coli, lambda phage, chiX174 phage, and simian virus 40. The low-molecular-weight protein ("E2-immunity protein") specifically prevented this in vitro DNA cleavage reaction, i.e., had an "immunity function." The results demonstrate that colicin E2 itself is a DNA endonuclease and explain the in vivo effects caused by E2 in sensitive cells as well as the mechanism of immunity in E2-colicinogenic cells.
Dynamic properties of isolated acetylcholine receptor protein: kinetics of the binding of acetylcholine and Ca ions.
Authors: Neumann E , Chang H W
Published: May 2006

Kinetic and thermodynamic constants for elementary steps associated with the interaction of acetylcholine (AcCh) and Ca with isolated AcCh receptor from Torpedo californica have been determined by chemical relaxation spectrometry. Murexide as used as a Ca indicator to monitor changes in Ca bound to the AcCh receptor. In the presence of AcCh this technique permits an indirect monitoring of AcCh binding, because the AcCh and the Ca binding reactions are competitively coupled. A temperature-jump perturbation in the Camurexide-AcCh receptor system induces a spectrum of relaxation processes characterized by at least three relaxation times: tau1 = 5 (+/-1) msec; tau2 = 35 (+/-5) msec; and tau3 = 300 (+/-30) msec. In the presence of AcCh, the Ca relaxation spectrum is altered in a characteristic way. A formalism is developed to describe the normal mode relaxation times of the coupled reaction system in terms of total concentrations of both AcCh and receptor binding sites. The analysis also allows one to determine the stoichiometry of the reactions involved or to estimate a molecular weight of the AcCh receptor. The kinetic data suggest that the reaction of AcCh with receptor proceeds in at least two steps. The rate constant of the association of AcCh with receptor was found to be 2.4(+/-0.5) X 10(7) M-1 sec-1 at 23.5 degrees, 0.1 M NaCl, 50 mM Tris-HCl, pH 8.5. Reaction schemes consistent with the present kinetic data are discussed in terms of physiocochemical model that accounts for the rapid transient conductivity changes in excitable membranes during nerve and muscle excitation.
Serinol as an activator of toxin production in attenuated cultures of
Helminthosporium sacchari
Authors: Pinkerton Frederick , Strobel Gary
Published: May 2006

Successive transfer in synthetic medium of spores and mycelial fragments from original toxin-producing cultures of
Helminthosporium sacchari
results in attenuated cultures which do not produce the host-specific toxin helminthosporoside. When attenuated cultures are grown on material obtained from the water wash of sugarcane leaves susceptible to this fungus, the production of heminthosporoside resumes. Compounds that activate toxin production in the fungus are present on the leaf surface and presumably arise via plant metabolism. One activator was identified as a novel free amine, serinol (2-amino-1,3-propanediol). It activates toxin production in attenuated cultures at 1 μM. Several experiments described in this report argue against the selection theory for the attenuation of cultures. The biological significance and some possible mechanisms for the activation of toxin biosynthesis are discussed.
Phytochrome-mediated
de novo
synthesis of phenylalanine ammonia-lyase: An approach using pre-induced mustard seedlings
Authors: Tong Wu-Fu , Schopfer Peter
Published: May 2006

The molecular mechanism of enzyme (phenylalanine ammonia-lyase; EC 4.3.1.5) formation mediated by phytochrome in mustard seedlings was investigated by labeling the enzyme with deuterium followed by high resolution CsCl density gradient analysis. A favorable relationship between induced rise of activity and turnover of this short-lived enzyme (half-life 3-4 hr) was achieved by labeling pre-irradiated seedlings. The time course of deuterium incorporation during the light-mediated rise in enzyme activity that can be derived independently from density shifts and bandwidth changes demonstrates a stimulation of synthesis and degradation by phytochrome. When synthesis is faster than degradation, enzyme accumulates.
Subcellualr distribution of protein carboxymethylase and its endogenous substrates in the adrenal medulla: possible role in excitation-secretion coupling.
Authors: Diliberto D J , Veiveros O H , Axelrod J
Published: May 2006

Protein carboxymethylase (S-adenosyl-L-methionine:protein O-methyltransferase, EC 2.1.1.24) transfers a methyl group from S-adenoxyl-L-methionine to carboxyl side chains of proteins to form labile protein-methyl esters which, thus, neutralize negative charges. This enzyme was examined for its possible participation in excitation-secretion coupling in the adrenal medulla. Protein carboxymethylase has a specific activity several times higher in the adrenal medulla than in the adrenal cortex; also, the medulla has a higher concentration of methyl-acceptor proteins. In the adrenal medulla, 97% of the enzyme was localized in the cytosol. Of the various subcellular fractions of the medulla, the catecholamine-containing chromaffin vesicles had the highest concentrations of substrat(s) for protein carboxymethylase. Carboxymethylation of proteins in intact chromaffin vesicles results in stripping of methylated protein(s) from the membranes. Thus, protein carboxymethylase appears to be involved in the neutralization of charges on the surface of chromaffin vesicles and in the release of surface proteins; both phenomena are likely to be required for exocytosis.
Infinite allele model with varying mutation rate.
Authors: Nei M , Chakraborty R , Fuerst P A
Published: May 2006

Available data suggest that the variation in mutation rate among protein loci follows the gamma distribution. Thus, taking into account this variation, formulae are developed for the distribution of allele frequencies, mean and variance of heterozygosity, expected number of alleles, proportion of polymorphic loci, and genetic distance. These formulae should be more appropriate for the analysis of gene frequency data for protein loci than equivalent formulae with constant mutation rate.
alpha-Adrenergic regulation of secretion of mouse saliva rich in nerve growth factor.
Authors: Wallace L J , Partlow L M
Published: May 2006

Nerve growth factor has been quantified by both bioassay and radial immunodiffusion in mouse saliva elicited by several secretagogues. The concentrations by bioassay of nerve growth factor in both epinephrine- and norepinephrine-induced saliva (3400 and 900 mug/ml, respectively) are higher than reported in any other source. In contrast, the concentrations of nerve growth factor in isoproterenol- and pilocarpine-induced saliva are relatively low (17 and 2 mug/ml, respectively). The specific activity of the salivary nerve growth factor was 41, 36, 2, and 0.6 mug/mg of protein in secretions elicited by epinephrine, norepinephrine, pilocarpine, and isoproterenol, respectively. Salivation after administration of either epinephrine or norepinephrine was completely inhibited by the alpha-adrenergic blocker, phenoxybenzamine. These results suggest that the release of saliva rich in nerve growth factor is primarily regulated through alpha-adrenergic receptors.
Rat sympathetic neurons and cardiac myocytes developing in microcultures: correlation of the fine structure of endings with neurotransmitter function in single neurons.
Authors: Landis S C
Published: May 2006

Microcultures containing single sympathetic principal neurons and small numbers of dissociated heart myocytes were prepared from newborn rats. After the transmitter properties of the neuron were studied by electrophysiological experiments, the microculture was examined with the electron microscope. Single neurons of either putative cholinergic or putative adrenergic character made morphological synapses on themselves (autapses), although only cholinargic autapses were detected electrophysiologically. Numerous axonal varicosities were present adjacent to the myocytes but no synaptic specializations were evident. After permanganate fixation to localize endogenous norepinephrine, the endings of neurons which appeared to secrete catecholamines contained many small granular vesicles, while the endings of neurons which appeared to secrete acetylcholine contained none. The endings of neurons which apparently secreted both catecholamines and acetylcholine contained only occasional small granular vesicles.
Allende meteorite: Isotopically anomalous xenon is accompanied by normal osmium
Authors: Takahashi H. , Higuchi H. , Gros Jacques , Morgan John W. , Anders Edward
Published: May 2006

The
184
Os/
190
Os ratio of six Allende meteorite samples was determined by neutron activation analysis. Four chromite concentrates gave a ratio differing from the terrestrial ratio by only -0.1 ± 0.4%, although they contained highly anomalous xenon enriched by up to 67% in
124
Xe and 93% in
136
Xe. In view of this result and the normal isotopic composition of carbon and oxygen in these fractions, it seems very unlikely that the xenon anomalies were produced in a supernova by the
p
and
r
processes. More probably, the xenon anomalies were established in the early solar system, by mass fractionation during trapping of noble gases in solids and by spontaneous fission of a superheavy element.

Two other samples, containing osmium from the calcium,aluminum-rich inclusions, also gave an
184
Os/
190
Os ratio within -0.1 ± 0.5% of the terrestrial value, although these inclusions show well-established anomalies in the light elements oxygen and magnesium, which appear to be due to pre-solar dust grains of distinctive nuclear history. Apparently the stellar source of the anomalous oxygen and magnesium did not synthesize heavier elements.
Segment-long-spacing aggregates and isolation of COOH-terminal peptides from type I procollagen.
Authors: Hoffmann H P , Olsen B R , Chen H T , Prockop D J
Published: May 2006

Type I procollagen secreted by matrix-free cells from chick embryo tendons was purified by DEAE-cellulose chromatography. Electron microscopy of segment-long-spacing aggregates of the procollagen demonstrated the presence of both NH2-terminal and COOH-terminal extensions not found in collagen. The procollagen was digested with bacterial collagenase and the COOH-terminal fragments were isolated by gel filtration and polyacrylamide gel electrophoresis in sodium dodecyl sulfate. Analysis of tryptic peptides demonstrated that the COOH-terminal extensions on the pro alpha 1 and pro alpha 2 chains had different primary structures.
Demonstration of a transitory tight binding of ATP and of committed P
i
and ADP during ATP synthesis by chloroplasts
Authors: Smith Daniel J. , Boyer Paul D.
Published: May 2006

Rapid mixing, quenching, and filtration experiments with chloroplast thylakoid membranes, with energization by acid-base transition, demonstrate that an ATP tightly bound to the isolated membranes is a transient intermediate in the catalytic sequence for ATP synthesis. The experiments also show that most of the P
i
and ADP bound at a catalytic site is committed to ATP formation without interchange with medium P
i
or ADP. Other results give evidence that upon energization, the tightly bound ADP that is detectable in isolated thylakoid membranes or coupling factor ATPase is rapidly released to the medium from a catalytic site. These findings support an alternating site model in which an energy-requiring conformational transition loosens ATP binding at one site and simultaneously promotes P
i
and ADP binding at the other site in a manner favoring ATP formation.
Adrenal cholesterol uptake from plasma lipoproteins: regulation by corticotropin.
Authors: Gwynne J T , Mahaffee D , Brewer H B , Ney R L
Published: May 2006

The transfer of lipoprotein-bound cholesterol into adrenal cells was examined. Adrenal glands from unstimulated or corticotropin stimulated hypophysectomized rats were incubated with high density lipoprotein (HDL) or low density lipoprotein LDL containing radiolabeled cholesterol. The rate of transfer of labeled cholesterol from HDL into the glands was two to three times greater than from LDL. Corticotropin stimulation increased the transfer of cholesterol from HDL but not LDL. The effects of corticotropin were not dependent on subsequent cholesterol utilization for steroidogenesis. The process of cholesterol transfer from HDL was linear with time over 2 hr at 37 degrees and greatly reduced at 4 degrees. In addition, the transfer process became saturated above an HDL cholesterol concentration of 900 mug/ml. About 25% of the labeled adrenal cholesterol arising from HDL was recovered within the mitochondria. The labeled cholesterol within isolated mitochondria could undergo mitochondrial conversion to pregnenolone. Finally, the delipidated HDL apolipoproteins, apoA-I and apoA-II, when added to incubations containing less than saturating concentrations of HDL, stimulated transfer of labeled cholesterol from HDL to adrenal cells. These studies suggest that rat adrenal tissue possesses an HDL specific hormonally-responsive mechanism for accumulating extracellular cholesterol and that apoA-I and apoA-II have a significant function in the uptake process.
Coupling of catecholamine receptor from one cell with adenylate cyclase from another cell by cell fusion.
Authors: Orly J , Schramm M
Published: May 2006

The experiments test the hypothesis that beta-adrenergic receptor is an independent unit that can be transferred from one adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4-6-1-1[ system to another. Turkey erythrocytes in which the catalytic activity of adenylate cyclase had been inactivated by N-ethylmaleimide or by heat contributed the beta-adrenergic receptor. Friend erythroleukemia cells (F cells) that possessed no measurable beta-adrenergic receptor contributed the adenylate cyclase. The erythrocytes in which the enzyme had been inactivated were fused with the F cells by Sendai virus. The cell ghosts of the fused preparation demonstrated adenylate cyclase activity which was strikingly enhanced by isoproterenol. Controls of fusion of F cells with each other or with human erythrocytes failed to show a response to isoproterenol. It was therefore concluded that the beta-adrenergic receptor of the turkey erythrocytes must have become functionally coupled to the adenylate cyclase of the mouse F cells. Activation by isoproterenol was demonstrable within a few minutes after fusion, and inhibitors of protein synthesis had no effect. Thus, coupling must have occurred between the preexisting components. The findings suggest that it may be possible in the future to confer on cells that possess an adenylate cyclase system new hormonal responses by inserting a receptor into their cell membrane. It is proposed that the procedure of massive heterologous cell fusion, as used in the present study, can be used to analyze the function of other cell membrane components.
Translation of turnip yellow mosaic virus RNA in vitro: a closed and an open coat protein cistron.
Authors: Pleij C W , Neeleman A , van Vloten-Doting L , Bosch L
Published: May 2006

Sucrose gradient centrifugation of heat-denatured RNA of turnip yellow mosaic virus permitted the isolation of five RNA classes with molecular weights ranging from 2.0 to 0.25 X 10(6). The infectivity was shown to be confined to an RNA molecule of molecular weight 2.0 X 10(6). No significant increase in infectivity was obtained by combination of the latter RNA with the RNA classes of smaller size. Translation in vitro of the RNAs of different size classes in a wheat germ cell-free system revealed that the infectious RNA (molecular weight 2.0 X 10(6) does not promote the synthesis of the coat protein of turnip yellow mosaic virus. Efficient production of this coat protein was found exclusively when the smallest RNA class (molecular weight 250,000) was used as a messenger. It is concluded that RNA molecules of turnip yellow mosaic virus of molecular weight 2.0 X 10(6) contain a closed coat protein cistron and that RNA molecules of molecular weight about 2 to 3 X 10(5) with an open coat protein cistron can be isolated from the virions.
Distribution of 3':5'-cyclic AMP and 3':5'-cyclic GMP in rabbit retina in vivo: selective effects of dark and light adaptation and ischemia.
Authors: Orr H T , Lowry O H , Cohen A I , Ferrendelli J A
Published: May 2006

By use of highly sensitive radioimmunoassays, 3':5'-cyclic AMP (cAMP) and 3':5'-cyclic GMP (cGMP) were measured in individual layers of light- and dark-adapted rabbit retinas, and the effects of ischemia were determined. In light-adapted retinas, cGMP levels ranged 50-fold, with over 90% of the total concentrated in the photoreceptor cells. The layer of outer segments contained 95 mumol/kg of dry weight, or three times the concentration present in the remainder of the photoreceptor cell layers. By contrast, levels of cAMP varied only 4-fold; the lowest level (6 mumol/kg of dry weight) was found in the outer segment layer and the highest level (22 mumol/kg of dry weight) in the inner segment layer of the photoreceptor cells. Dark adaptation elevated cGMP levels only in retinal layers containing photoreceptor cells, and the greatest proportional increase was observed in the synaptic layer of photoreceptor cells. Dark adaptation also caused increases of cAMP that were restricted to the outer plexiform and outer nuclear layers. Ischemia lowered cGMP levels, but only in retinal layers containing photoreceptor cells, and elevated cAMP levels, primarily in the inner layers of the retina. The effects of ischemia were greater in the dark-adapted than in light-adapted retinas. These results indicate that cGMP and cAMP levels in retina are influenced by the light adaptational state, that ischemia markedly modifies these processes, and that the effects of both light exposure and ischemia are regionally selective.
Changes in cellular glycoproteins after transformation: identification of specific glycoproteins and antigens in sodium dodecyl sulfate gels.
Authors: Burridge K
Published: May 2006

The glycoproteins of whole cells have been analyzed by direct application of radio-iodinated lectins to sodium dodecyl sulfate gels, followed by autoradiography. By use of lectins with different carbohydrate specificities, different sets of glycoproteins have been visualized. The most prominent lectin-binding band in many gels is thelarge, external, transformation-sensitive (LETS) protein. Major glycoprotein differences are revealed when normal and virus-transformed cells are compared. Certain differences, however, are also seen when the glycoproteins are compared from two separately derived simian virus 40 transformants of 3T3 cells, suggesting a degree of clonal variation between these lines that may not relate to transformation. A complementary technique is used to detect specific antigens in sodium dodecyl sulfate gels by direct application of iodinated antibodies. An antiserum specific for the LETS protein is used to identify this antigen in the gels of both normal and transformed cells.
Development of the photosynthetic unit in lettuce
Authors: Henriques Fernando , Park Roderic B.
Published: May 2006

A comparative study of polypeptide composition and freeze-fracture morphology of chloroplast membranes isolated from different, but photosynthetically active, regions of a romaine lettuce shoot is presented. Chloroplasts prepared from outer dark-green leaves possess a fully developed light-harvesting chlorophyll-protein complex, have low chlorophyll
a
:
b
ratios and display fracture faces similar to those found in other higher plant chloroplast membranes; chloroplasts from leaves more to the interior of the shoot, have a much lower content of chlorophyll, show high chlorophyll
a
:
b
ratios, are depleted in components of the light-harvesting chlorophyll-protein complex, and exhibit extensive modifications of their fracture faces. We have also re-examined the freeze-fracture morphology of chloroplast membranes from a barley
b
-deficient mutant that lacks the light-harvesting chlorophyll-protein complex. A tentative interpretation of our findings suggests correlating the assembly of the light-harvesting chlorophyll-protein complex into the chloroplast membranes with the appearance of large freeze-fracture B face particles in the stacked interior-membrane region, and differentiation of typical fracture faces.
Single burst study of rec- and red-mediated recombination in bacteriophage lambda.
Authors: Sarthy P V , Meselson M
Published: May 2006

Single bursts from three-point crosses of bacteriophage lambda were analyzed for recombination of markers several thousand nucleotide pairs apart. Single recombination, mediated by the rec system of Escherichia coli, is usually reciprocal. Double recombinants are also significantly correlated in single bursts, although the correlation is weaker than for reciprocal singles. Reciprocity is not found in crosses mediated by the lambda red system. With respect to certain other paraments of recombination, the two systems appear to be alike. Double recombinants usually result from one event, not from two independent single recombinations, and their average clone size is about half that of single recombinants. The results are discussed in terms of current molecular models of recombination.
Occurrence of BK virus DNA in DNA obtained from certain human tumors.
Authors: Fiori M , Di Mayorca G
Published: May 2006

DNA sequences from BK virus have been detected by measurements of reassociation kinetics in DNA preparations isolated from five of 12 human tumor tissues and three of four human tumor cell lines; no DNA sequences from BK virus could be found using the same assay in DNA samples obtained from nontumor tissues removed from various patients. Whether or not this association is trivial, indicative of infection by BK virus, or correlative with the tumor state must await the testing of additional samples of normal and tumor tissues as well as a definition of the physical state of the genome of BK virus.
Direct determination of surface tension in the lung.
Authors: Schürch S , Goerke J , Clements J A
Published: May 2006

We have used the spreading behavior of small drops of several fluorocarbon fluids and silicone oil on air-liquid interfaces to measure the surface tension of lungs in situ. The test fluids were calibrated in a surface balance at 37 degrees on monolayers of dipalmitoylphosphatidylcholine. At particular surface tensions characteristic of each fluid used, an increase in the tension of 1 mN/m or less caused the droplets to spread reversibly from a sphere to a lens shape. Using micropipettes we placed such droplets on the alveolar surfaces of excised rat lungs held at functional residual capacity and 37 degrees and found that the surface tension remained below 9 mN/m for at least 30 min. The surface tension-volume relationship was linear for tensions ranging from 9 to 20 mN/m.
Intramolecular energy transfer and molecular conformation.
Authors: Dale R E , Eisinger J
Published: May 2006

A discussion of the range of applicability of Forster long-range energy transfer in the determination of macromolecular dimensions and conformational dynamics is given. Emphasis is laid on the effect of restrictions in the orientational freedom of donor and acceptor and on the importance of the orientational averaging regime. The usefulness and limitations of polarized emission measurements in this regard are discussed.
Studies on secondary structure of single-stranded RNA from bacteriophage MS2 by electron microscopy.
Authors: Jacobson A B
Published: May 2006

A method allowing the demonstration and study by electron microscopy of secondary structure of viral RNA has been developed. Single-stranded RNA from the bacteriophage MS2 has been analyzed in the electron microscope in the presence of various concentrations of MgCl2. Depending on the salt concentration, the molecules display one to three large open loops which range in size from 10 to 20% of the total RNA length, and smaller closed loops which are approximately 3-5% of the total RNA length. Within one spreading, the conformation of the molecules is variable. However, the average complexity of the molecules increases with increasing salt, and individual loops which are infrequent at low salt increase in frequency with increasing salt. By analyzing the manner in which the individual loop appeared, it was possible to show that all molecules could be described by one basic pattern of secondary structure formation.
Stoichiometric relationship between energy-dependent proton ejection and electron transport in mitochondria.
Authors: Brand M D , Reynafarje B , Lehninger A L
Published: May 2006

The number of protons ejected during electron transport per pair of electrons per energy-conserving site (the H+/site ratio) was measured in rat liver mitochondria by three different methods under conditions in which transmembrane movements of endogenous phosphate were minized or eliminated. (1) In the Ca2+ pulse method, between 3.5 and 4.0 molecules of 3-hydroxybutyrate and 1.75 to 2.0 Ca2+ ions were accumulated per 2 e- per site during Ca2+ induced electron transport in the presence of rotenone, when measured under conditions in which movements of endogenous phosphate were negligible. Since entry of 3-hydroxybutyrate requires its protonation to the free acid these data correspond to an H+/site ratio of 3.5-4.0 (2) In the oxygen pulse method addition of known amounts of oxygen to anaerobic mitochondria in the presence of substrate yielded H+/site ratios of 3.0 when phosphate transport was eliminated by addition of N-ethylmaleimide or by anaerobic washing to remove endogenous phosphate. In the absence of such measures the observed H+/site ratio was 2.0. (3) In the reductant pulse method measurement of the initial steady rates of H+ ejection and oxygen consumption by mitochondria in an aerobic medium after addition of substrate gave H+/site near 4.0 in the presence of N-ethylmaleimide; in the absence of the inhibitor the observed ratio was only 2.0. These and other experiments reported indicate that the values of 2.0 earlier obtained for the H+/site ratio by Mitchell and Moyle [Biochem J. (1967) 105, 1147-1162] and others were underestimates due to the unrecognized masking of H+ ejection by movements of endogenous phosphate. The results presented here show that the H+/site ratio of mitochondrial electron transport is at least 3.0 and may be as high as 4.0.