bluuebunny/crossref_metadata_2025 huggingface dataset:
Cordycepin Inhibits Induction of Murine Leukovirus Production By 5-Iodo-2′-deoxyuridine
Authors: Wu A. M. , Ting R. C. , Paran M. , Gallo R. C.
Published: May 2006

Cordycepin (3′-deoxyadenosine), an inhibitor of poly(A) synthesis during the processing of nuclear heterogenous RNA, blocks the production of RNA viruses induced by 5-iodo-2′-deoxyuridine in BALB/3T3 and BALB/K-3T3 cells. This inhibitory activity is not a result of either nonspecific cell killing or general cytotoxicity by cordycepin; rather, it appears to be specific, because cordycepin acts only at a critical time to inhibit virus production. These findings, together with the finding of poly(A) sequences in viral RNAs, suggest that RNA tumor viruses replicate via a transcription of proviral DNA.
Inhibition of Release of Dopamine-β-Hydroxylase and Norepinephrine from Sympathetic Nerves by Colchicine, Vinblastine, or Cytochalasin-B
Authors: Thoa Nguyen B. , Wooten G. Frederick , Axelrod Julius , Kopin Irwin J.
Published: May 2006

Stimulation of the hypogastric nerve to the guinea pig vas deferens in the presence of phenoxybenzamine produced an enhanced release of both dopamine-β-hydroxylase (EC 1.14.2.1) and norepinephrine. Addition of colchicine, vinblastine, or cytochalasin-B to the incubation medium caused an almost complete inhibition of release of both the amine and the enzyme. Colchicine and cytochalasin-B produced a blocking effect but did not, however, modify the ratio of dopamine-β-hydroxylase to norepinephrine recovered in the bath fluid. The findings indicate that norepinephrine and dopamine-β-hydroxylase are released from sympathetic nerve terminals by exocytosis and that this process is dependent upon the integrity of both microtubules and microfilaments.
Insulin Receptors in Human Circulating Cells and Fibroblasts
Authors: Gavin James R. , Roth Jesse , Jen Phyllis , Freychet Pierre
Published: May 2006

Human lymphocytes obtained from fasted adult subjects and cultured human tumor lymphocytes were investigated for specific insulin receptors. By use of monoiodoinsulin, specific insulin binding sites were demonstrated in peripheral human lymphocytes, cultured human lymphocytes, and in other types of human circulating cells. Insulins and insulin derivatives that varied in their potency to stimulate glucose oxidation in the fat cell and to inhibit binding of [
125
I]insulin to purified plasma membranes, varied in an analogous fashion in their ability to inhibit the binding of labeled insulin to human lymphocytes. Hormones that had no effect on the binding of insulin to fat cells or liver membranes also had no effect on the binding of insulin to lymphocytes. Binding was time and temperature dependent; dissociation of [
125
I]insulin was rapid upon addition of 10 μM insulin. These findings afford a direct approach to the study of endocrine disorders in man.
Stimulation of Release of Adrenal Catecholamine by Adenosine 3′:5′-Cyclic Monophosphate and Theophylline in the Absence of Extracellular Ca
2+
Authors: Peach Michael J.
Published: May 2006

Stimulation of catecholamine release was studied in the isolated adrenal of the cat during retrograde perfusion. Theophylline, adenosine 3′:5′-cyclic monophosphate (cyclic AMP), and dibutyryl-cyclic AMP stimulated catecholamine release in adrenal chromaffin tissue; adenosine, 2′-AMP, 3′-AMP, and 5′-AMP were ineffective. Addition of theophylline for 5-15 min had no effect on catecholamine release induced by KCl or nicotine, but it significantly increased the responses to cyclic AMP and its dibutyryl derivative. Glands perfused with Ca
2+
-free Locke's solution for 30-180 min rapidly lost their responsiveness to KCl or nicotine. In contrast, exposure to Ca
2+
-free medium for 180 min had no effect on secretory responses to either the cyclic nucleotides, themselves, or to methylxanthine-induced potentiation of cyclic AMP responses. Thus, dibutyryl-cyclic AMP, cyclic AMP, and theophylline do not require extracellular Ca
2+
to release adrenal catecholamines. They may act by translocating intracellular bound Ca
2+
or by a mechanism independent of calcium.
Affinity Chromatography and Purification of the Insulin Receptor of Liver Cell Membranes
Authors: Cuatrecasas Pedro
Published: May 2006

Relatively simple and rapid procedures are described for the large-scale preparation of liver membranes that contain virtually all of the high affinity insulin-binding activity of liver homogenates. The presumed insulin recepotr, which is extracted from these membranes in soluble form with Triton X-100, can be further purified by ammonium sulfate fractionation (3-fold purification) or by diethylaminoethyl-cellulose chromatography (60-fold purification). Several insulin-agarose derivatives have been synthesized that can efficiently extract the insulin-binding protein from the detergent extracts of the membranes. The receptor macro-molecule can be eluted from the affinity columns in high (50-80%) yield by use of urea-containing buffers of moderately low pH. The receptor, thus purified by small-scale affinity chromatography experiments, approaches theoretical purity on the basis of its specific activity. This protein is purified about 250,000-fold from the liver homogenate by detergent extraction and affinity chromatography.
Cooperation of Mitochondrial and Nuclear Genes Specifying the Mitochondrial Genetic Apparatus in
Neurospora crassa
Authors: Barath Zoltan , Küntzel Hans
Published: May 2006

Enzymes involved in the expression of the mitochondrial genome in
Neurospora crassa
are induced by chloramphenicol and ethidium bromide, which block transcription and translation of mitochondrial DNA. It is concluded that most, if not all, proteins of the mitochondrial genetic apparatus are coded by nuclear genes, synthesized on cytoplasmic ribosomes, and controlled by a repressor-like mitochondrial gene product. A model explaining the coordination of nuclear and mitochondrial division cycles by repressor control is discussed.
Role of DNA and Specific Cytoplasmic Receptors in Glucocorticoid Action
Authors: Baxter John D. , Rousseau Guy G. , Benson M. Christina , Garcea Robert L. , Ito James , Tomkins Gordon M.
Published: May 2006

Glucocorticoids induce tyrosine aminotransferase (EC 2.6.1.5) synthesis in cultured rat hepatoma cells. These steroids penetrate the cell membrane and bind to specific cytoplasmic receptor proteins. The resulting complex binds to the nucleus. This nuclear binding has now been studied in a cell-free preparation. The reaction appears to require a temperature-dependent modification of the steroid-receptor complex. There is a fixed number of nuclear sites that are half saturated at a complex concentration of 6 to 24 × 10
-11
M. Treatment with deoxyribonuclease destroys nuclear-binding capacity. The complex also binds to purified HTC cell DNA with characteristics similar to the binding to isolated nuclei, and, as in intact cells, receptors complexed with an anti-inducer steroid bind very poorly to DNA. These data suggest that the nuclear sites for binding steroid-receptor complexes are on the DNA. Since the extent of complex binding to purified DNA exceeds that observed with isolated nuclei, chromosomal proteins may act to restrict binding to certain regions of the DNA. These studies suggest that steroid hormones stimulate the synthesis of specific proteins by affecting the transcription of structural or regulatory genes.
Biosynthesis of Acetylcholine in Turtle Photoreceptors
Authors: Lam Dominic M. K.
Published: May 2006

For determination of possible neurotransmitters synthesized by photoreceptor cells, turtle retinas were dissociated into single cells with proteolytic enzymes. These cells were partially separated by velocity sedimentation to yield a fraction rich in photoreceptors. Individual photoreceptor cells were then sucked into a micropipette and incubated with labeled precursors of known or suspected neurotransmitters. After incubation, the radioactive products were analyzed by high-voltage electrophoresis. Of all the chemicals tested, turtle photoreceptor cells synthesized only acetylcholine, suggesting that these cells may be cholinergic.
Serological Detection of a Cell-Surface Antigen Specified by the T (Brachyury) Mutant Gene in the House Mouse
Authors: Bennett Dorothea , Goldberg Ellen , Dunn L. C. , Boyse Edward A.
Published: May 2006

A cell-surface component specified by a mutant gene at the T-locus in the mouse has been detected on sperm by serological methods. The gene product thus recognized is not present on other adult cells.
Calcium-Dependent Norepinephrine Release from Presynaptic Nerve Endings
In Vitro
Authors: Blaustein Mordecai P. , Johnson Eugene M. , Needleman Philip
Published: May 2006

Potassium concentrations above 15-20 mM in the medium, or addition of 75 μM veratridine to medium that contains 5 mM K, stimulate calcium accumulation and Ca-dependent norepinephrine release by presynaptic nerve terminals (synaptosomes) incubated
in vitro
. The effects of veratridine, but not of K, are blocked by 0.2 μM tetrodotoxin. This association between Ca entry and norepinephrine release is consistent with the Calcium Hypothesis of transmitter release. These results add further evidence that synaptosomes may retain many functional properties of intact presynaptic endings.
Control of Daughter-Cell Number Variation in Multiple Fission: Genetic versus Environmental Determinants in
Prototheca
Authors: Poyton Robert O. , Branton Daniel
Published: May 2006

Prototheca zopfii
has been developed as an experimental system for studying the control of cytokinesis and daughter-cell number variation in multiple fission. Although mean daughter-cell number increases linearly with growth rate, and this dependency is genetically controlled, pedigree analysis shows that daughter-cell number
variation
is not under direct genetic control. In a population growing in steady-state balanced growth, each cell has a given probability of dividing into 2, 4, 8 16, or 32 daughter-cells. These probabilities are independent of the division number of the cell in the preceding generation, and can be altered by changes in the culture medium.
Glycerol as an Enzyme-Stabilizing Agent: Effects on Aldehyde Dehydrogenase
Authors: Bradbury Shelby L. , Jakoby William B.
Published: May 2006

The potassium-dependent aldehyde dehydrogenase (EC 1.2.1.3), from yeast is markedly altered by the addition of high concentrations of glycerol or other polyhydric alcohols to aqueous buffers. Several lines of evidence suggest that the three-dimensional structure near the active site is involved: (
i
) The stability of the enzyme when stored at 2°, or when subjected to repeated freezing and thawing, depends upon the presence of at least 30% (v/v) glycerol. (
ii
) In the same solvent, the

K
m

value for DPN and the binding constant for benzaldehyde decrease by 3- and 10-fold, respectively, compared with the values obtained for these substrates in fully aqueous media. (
iii
) Competitive inhibition by trivalent arsenicals with respect to DPN is no longer observed in glycerol; the inhibition becomes mixed and the

K
i

values increase by 5- and 50-fold, respectively, with arsenite and Mapharsen. (
iv
) Essential sulfhydryl groups, which are easily carboxymethylated in aqueous buffers, are not readily available in either glycerol or mannitol.

The data are consistent with a change in topography induced by polyhydric alcohols in which sulfhydryl groups near the DPN-binding site are displaced to a more protected environment, where their reactivity is reduced. Since the stabilizing effects of such alcohols are frequently encountered, these results may have application to other enzymes.
Lac
Operator Analogues: Bromodeoxyuridine Substitution in the
lac
Operator Affects the Rate of Dissociation of the
lac
Repressor
Authors: Lin Syr-Yaung , Riggs Arthur D.
Published: May 2006

As measured by a decreased rate of dissociation,
lac
repressor binds 10-times tighter to 5-bromodeoxyuridine-substituted
lac
operator than it does to normal
lac
operator. This result is obtained both in the absence and in the presence of isopropylthiogalactoside, an inducing ligand. These data are significant with regard to the mechanism of sequence-specific protein-DNA interaction, and also suggest a possible explanation for the effects of bromodeoxyuridine on the expression of differentiated functions in eukaryotic cells.
Influence of Valinomycin on Circadian Leaf Movements of
Phaseolus
Authors: Bünning E. , Moser I.
Published: May 2006

Phaseolus coccineus
was exposed to valinomycin via the transpiration stream for 5-hr periods. The treatment started at various phases of the free-running circadian rhythm in continuous light; it resulted in phase shifts that varied in a manner dependent on the affected phases. The response curves are similar to those for transient withdrawal of water and for light pulses. The results support the hypothesis that membrane processes are important pacemakers in circadian rhythms.
Weaver Mutant Mouse Cerebellum: Defective Neuronal Migration Secondary to Abnormality of Bergmann Glia
Authors: Rakic P. , Sidman R. L.
Published: May 2006

Previous work showed that in cerebella of mice homozygous for the autosomal mutation weaver,
wv
, most postmitotic granule cell neurons die during the first 2 weeks after birth close to their site of genesis in the external granular layer. Analysis of the less severely affected heterozygotes by electron microscopy and autoradiography indicates that granule cell death occurs several days after cell genesis and is secondary to failure of their somas to migrate across the molecular layer to the granular layer. This migration defect in turn appears secondary to a hitherto unrecognized disorder of Bergmann glial cells, the cells that normally guide the young neurons in their migration. In +/
wv
cerebella, Bergmann glial processes are enlarged and irregular in caliber, electronlucent, and often vacuolated; in
wv/wv
, Bergmann cell processes are almost absent. The primary genetic abnormality remains undefined, but the gene dosage effect, here recognized at a cellular level for the first time in a mammalian neurological mutant, suggests that even though neuronal death serves as the most prominent and clinically relevant phenotypic expression, the Bergmann glial abnormality may actually be closer to the primary cellular target of the
wv
genetic locus.
Development of Acetylcholine Receptor Clusters on Cultured Muscle Cells
Authors: Sytkowski A. J. , Vogel Z. , Nirenberg M. W.
Published: May 2006

Clusters of acetylcholine receptors were formed in the absence of neurons during the development of cultured chick-embryo skeletal muscle cells. The average concentration of receptors in clusters was estimated to be 9000 per μm
2
. At other regions of the cell, receptor concentration was 900 per μm
2
. The possibility that receptor clusters may participate in synapse formation is suggested.
Plasma Aggregating Factor (Bovine) for Human Platelets: A Marker for Study of Antihemophilic and von Willebrand Factors
Authors: Griggs Thomas R. , Cooper Herbert A. , Webster William P. , Wagner Robert H. , Brinkhous K. M.
Published: May 2006

The human-platelet aggregating factor in preparations of bovine plasma and bovine antihemophilic factor has been reported to be an activity of bovine antihemophilic factor. However, we show that activities of aggregating factor and antihemophilic factor are present in varying proportion in different preparations of antihemophilic factor. Aggregating factor activity is more stable on storage than is antihemophilic factor activity and can be selectively adsorbed by human platelets. Further, antihemophilic factor activity free of aggregating activity was eluted from DEAE-Sephadex. The factors were also separated during agarose chromatography in 0.25 M CaCl
2
, which yields a small-molecular-weight moiety with antihemophilic factor activity; aggregating factor activity continued to elute in the void volume. Thus, aggregating factor activity is clearly separable from antihemophilic factor activity. The usual physiologic platelet-aggregating reactions require fresh platelets. Fresh, aged, and sonicated platelets, but not platelets that have been frozen and thawed, react with aggregating factor, indicating that the platelet “receptor sites” for the aggregating factor are unusually stable.
Identification of Chick Chromosomes in Cell Hybrids Formed Between Chick Erythrocytes and Adenine-Requiring Mutants of Chinese Hamster Cells
Authors: Kao Fa-Ten
Published: May 2006

When chick erythrocytes were fused with adenine-requiring mutants of Chinese hamster cells of two different complementation classes and grown in adenine-free medium for 1 week or longer, mitotic cells were observed containing both chick and Chinese hamster metaphase chromosomes within a single cell. Stable hybrid clones were subsequently isolated that possessed, in addition to a complete Chinese hamster genome, a single specific chick chromosome. Hybrids resulting from fusions involving different adenine mutants retained different, identifiable chick chromosomes. Thus, the two chick genes for the endogenous synthesis of adenine were assigned to the respective chick chromosomes.
Isolation of
Escherichia coli
RNA Polymerase Binding Sites on T5 and T7 DNA: Further Evidence for Sigma-Dependent Recognition of A-T-Rich DNA Sequences
Authors: Talaer J. Y. Le , Kermici M. , Jeanteur Ph.
Published: May 2006

Previous isolation and analysis of
E. coli
RNA polymerase (EC 2.7.7.6) binding sites on λ DNA had demonstrated the existence of a sigma-dependent process of recognition of A-T-rich DNA sequences. We have now extended this finding to T5 and T7 DNA and häve provided evidence for the double-strandedness of the isolated binding sites. The possible equation of these sites to the genetically defined promoters is discussed.
Dynamics of Metabolism of Normal and Virus-Transformed Chick Cells in Culture
Authors: Bissell M. J. , White R. C. , Hatie C. , Bassham J. A.
Published: May 2006

Application of steady-state tracer technique to normal and transformed cells in tissue culture allows quantitation of intracellular pool sizes of many metabolites and determination of rate of carbon flow along diverse paths. Using a unique apparatus to control the environmental conditions, we show that the glucose carbon flow into tricarboxylic acid cycle intermediates and amino acids is unchanged upon transformation. The increased glycogen formation and glycolysis varies with the glucose concentration in the medium, correlates with the faster glucose transport of transformed cells, and cannot be explained by a difference in growth rate alone.
Membrane Optical Activity: Some Facts and Fallacies
Authors: Wallach Donald F. H. , Low David A. , Bertland Alexander V.
Published: May 2006

The circular dichroism of hypothetical, water-filled, spherical shells, 75-3500 nm in radius, with walls 7.5 nm thick, composed of poly(L-lysine) in various conformational proportions, and suspended in water, were computed from the known optical properties of this polypeptide by classical general light-scattering theory (Mie theory). Comparison of the computed curves of circular dichroism spectra with those of diverse membranes reveals large discrepancies below 215 nm and shows that light scattering does not adequately account for the optical activity of membranes containing appreciable proportions of nonhelical conformation. However, turbidity effects can explain the anomalies of membrane optical rotatory dispersion near 233 nm, if not uniquely so. We conclude that the optical activity of neither most soluble proteins nor membrane proteins can provide accurate conformational information when synthetic polypeptides are used as standards and list the reasons for this argument. We also show that present techniques to “correct” membrane optical activity are likely to produce additional artifact.
Separate Intramolecular Pathways for Reduction and Oxidation of Cytochrome
c
in Electron Transport Chain Reactions
Authors: Margoliash E. , Ferguson-Miller Shelagh , Tulloss J. , Kang Chae Hee , Feinberg B. A. , Brautigan D. L. , Morrison M.
Published: May 2006

The monoiodotyrosine 74, formyltryptophan 59, mononitrotyrosine 67, and carboxymethylmethionine 80 derivatives of horse cytochrome
c
are defective in their ability to accept electrons from the succinate-cytochrome
c
reductase system, while their reactions with purified cytochrome
c
oxidase are essentially those of the native protein. The 4-nitrobenzo-2-oxa-1,3-diazole derivative of lysine 13 of horse cytochrome
c
and the bis-phenylglyoxal derivative of arginine 13 of
Candida krusei
cytochrome
c
have the opposite properties, in that they are readily reduced by the succinate-cytochrome
c
reductase (EC 1.3.99.1) system but are defective in their capability of transferring electrons to cytochrome
c
oxidase (EC 1.9.3.1). We conclude that electrons from mitochondrial cytochrome
c
reductase are transmitted to ferricytochrome
c
by a different pathway than electrons from ferrocytochrome
c
to cytochrome
c
oxidase. The present results are compatible with the concept that the mechanism of reduction involves an aromatic ring channel comprising residues 74, 59, 67, and 80, leading from the “left back” part of the protein to the heme iron. On the other hand, since residue 13 is immediately above the edge of the heme that is at the “front surface” of the molecule, we suggest that the electron leaves ferrocytochrome
c
to cytochrome
c
oxidase by way of the edge of pyrrole ring II or the adjacent surface-located sulfur of cysteinyl residue 17, which is thioether bonded to the heme. On this basis, the sites of electron entry and exit in cytochrome
c
would appear to be some 110° of arc away from each other along the surface of the protein, explaining several previously observed phenomena.
Role of Guanine Nucleotides in Protein Synthesis. Elongation Factor G and Guanosine 5′-Triphosphate,3′-Diphosphate
Authors: Hamel Ernest , Cashel Michael
Published: May 2006

The possible role of guanosine 5′-triphosphate,3′-diphosphate (pppGpp) in protein synthesis by
Escherichia coli
ribosomes and protein factors was examined. Although pppGpp could effectively substitute for GTP in reactions catalyzed by initiation factor 2 (ribosomal binding of fMet-tRNA and formation of
N
-formylmethionylpuromycin) and elongation factor T (ribosomal binding of Phe-tRNA and formation of dipeptidyl-tRNA), pppGpp poorly supported polyphenylalanine synthesis. The interaction of elongation factor G with pppGpp was, therefore, examined in detail. The nucleotide was found to be almost without activity in the translocation reaction, as measured by formation of
N
-acetylphenylalanyl-phenylalanylpuromycin. Nevertheless, the rate of the catalytic hydrolysis of pppGpp to guanosine 5′-diphosphate,3′-diphosphate by elongation factor G and ribosomes was about 30% of the rate of hydrolysis of GTP, a rate of hydrolysis that significantly exceeded the rate of translocation with GTP. Moreover, the rates of the fusidic acid-dependent, elongation factor G-dependent binding of pppGpp and ppGpp to ribosomes were about 75 to 85% the rates of GTP and GDP binding, respectively. We also found that dGTP could substitute for GTP in all reactions examined.
Potentiation by Endotoxin of Responses Associated with Increases in Calcium Conductance
Authors: Connor John , Fine Jacob , Kusano Kiyoshi , Mccrea Mary Jacobs , Parnas I. , Prosser C. L.
Published: May 2006

Bacterial endotoxin at concentrations of 0.03 μg/ml enhanced the following responses, each of which reflects calcium influx: (
1
) contraction of spiral intestine retractor muscle of dogfish; (
2
) amplitude of postsynaptic potential of squid giant synapse as a function of presynaptic depolarization; (
3
) membrane responses of deep abdominal extensor muscle of crayfish, stimulated intracellularly; and (
4
) slow transient (calcium) current in trabeculae of frog atrium under voltage clamp. Corticosteroid antagonized the endotoxin effect on the smooth muscle, not on the frog atrial current. One mechanism of action of endotoxin may be to increase transmembrane calcium currents.
The Nucleotide Sequence of the
lac
Operator
Authors: Gilbert Walter , Maxam Allan
Published: May 2006

The
lac
repressor protects the
lac
operator against digestion with deoxyribonuclease. The protected fragment is double-stranded and about 27 base-pairs long. We determined the sequence of RNA transcription copies of this fragment and present a sequence for 24 base pairs. It is: 5′--T G G A A T T G T G A G C G G A T A A C A A T T 3′ 3′--A C C T T A A C A C T C G C C T A T T G T T A A 5′ The sequence has 2-fold symmetry regions; the two longest are separated by one turn of the DNA double helix.
The Affinity-Labeling of Partially Purified Acetylcholine Receptor from Electric Tissue of
Electrophorus
Authors: Karlin Arthur , Cowburn David
Published: May 2006

The receptor for acetylcholine was partially purified by affinity chromatography of an extract in Triton X-100 of membrane fragments from electric tissue. The receptor was assayed, after its reduction with dithiothreitol, by reaction with the affinity-alkylating agent, [
methyl
-
3
H]4-(
N
-maleimido)-benzyltrimethylammonium iodide. Alternative labeling procedures, one useful for routine assay of picomole quantities of receptor and the other for labeling larger quantities of receptor, are described. The purified receptor specifically incorporated about 3 nmol of label per mg of protein. This incorporation was blocked by pretreatment of the receptor with
Naja naja siamensis
neurotoxin. The rate of the affinity reaction was similar to that found with membrane fragments and with intact electroplax. Furthermore, as in intact electroplax, [
3
H]4-(
N
-maleimido)-benzyltrimethylammonium iodide reacted 5000-fold faster with the reduced receptor than did [
14
C]
N
-ethylmaleimide. When purified receptor was labeled with [
3
H]4-(
N
-maleimido)-benzyltrimethylammonium iodide and subjected to electrophoresis on polyacrylamide gels in dodecyl sulfate and dithiothreitol, three major protein bands were observed. Only one of these, however, contained
3
H activity; its mobility indicated a molecular weight of 40,000.
DNA Methylase Induced by Bacteriophage ϕX174
Authors: Razin Aharon
Published: May 2006

A cytosine-specific DNA methylase activity, which is normally absent in the
Escherichia coli
B strain, was found to be induced in these cells by infection with bacteriophage ϕX174.
In vivo
experiments revealed a single 5-methylcytosine residue in the phage DNA molecule and 5-methylcytosine residues in the infected host DNA, in addition to the 6-methylaminopurine residues present in the uninfected cells.
In vitro
, a partially purified enzyme from infected cells methylated DNA from uninfected cells, but showed no activity with cellular DNA from infected cells. The partially purified methylase derived from uninfected cells lacks this activity.
Myosin ATP Hydrolysis: A Mechanism Involving a Magnesium Chelate Complex
Authors: Burke Morris , Reisler Emil , Harrington William F.
Published: May 2006

It is suggested that under physiological conditions (> 1 mM Mg
2+
) MgATP binds to myosin to form a chelate involving the two reactive sulfhydryl sites (SH
1
and SH
2
). The stability of the chelate structure results in marked inhibition of the myosin ATPase in the presence of millimolar magnesium ion. The inhibitory effect of magnesium ion can be eliminated chemically by blocking either the SH
1
or SH
2
site since this precludes formation of the chelate. In muscle, actin apparently behaves in a similar fashion in that its interaction with myosin causes a disruption of the chelate structure.
Hydrophobicity of Long Chain
n
-Alkyl Carboxylic Acids, as Measured by Their Distribution Between Heptane and Aqueous Solutions
Authors: Smith Ross , Tanford Charles
Published: May 2006

Previous data for the distribution of the
n
-alkyl carboxylic acids between aqueous buffers and heptane have suggested that the free energy of transfer between the two solvents does not increase with the length of the alkyl chain beyond palmitic acid, indicating a limit to the hydrophobicity of the alkyl chain at a length of about 15 carbon atoms. It is shown in this paper that previous measurements were influenced by unexpectedly strong pH-dependent association of the long-chain acids in the aqueous phase. Under conditions where such association becomes negligible, the free energy of transfer becomes a strictly linear function of alkyl chain length for all acids up to behenic acid (C
21
H
43
COOH).
Temperature Adaptation of Enzymes: Roles of the Free Energy, the Enthalpy, and the Entropy of Activation
Authors: Low Philip S. , Bada Jeffrey L. , Somero George N.
Published: May 2006

The enzymic reactions of ectothermic (cold-blooded) species differ from those of avian and mammalian species in terms of the magnitudes of the three thermodynamic activation parameters, the free energy of activation (Δ
G
⧧
), the enthalpy of activation (Δ
H
⧧
), and the entropy of activation (Δ
S
⧧
). Ectothermic enzymes are more efficient than the homologous enzymes of birds and mammals in reducing the Δ
G
⧧
“energy barrier” to a chemical reaction. Moreover, the relative importance of the enthalpic and entropic contributions to Δ
G
⧧
differs between these two broad classes of organisms.
Contraction of Isolated Smooth-Muscle Cells—Structural Changes
Authors: Fay Fredric S. , Delise Claudio M.
Published: May 2006

The contraction of isolated smooth-muscle cells has been correlated with evagination of the cell membrane, a marked change in myofilament orientation, and a decrease in cellular volume. Both localized and full contractions have been elicited in the same cell by varying the intensity of electrical stimulation. These results may be explained by a model of the smooth-muscle cell in which the contractile apparatus extends between attachment sites on the cell membrane that are relatively closely spaced.
Roles of Calcium, Serum, Plasma, and Folic Acid in the Control of Proliferation of Normal and Rous Sarcoma Virus-Infected Chicken Fibroblasts
Authors: Balk S. D. , Whitfield J. F. , Youdale T. , Braun Armin C.
Published: May 2006

In a culture medium of pH 7.4 and a folic acid concentration of 100 μg/liter that contains 5% heat-inactivated chicken plasma rather than serum, the rate of proliferation of normal chicken fibroblasts is determined by the concentration of calcium. Proliferation, rapid when the calcium concentration is physiological, decreases when the calcium concentration is reduced. At a very low calcium concentration, in this culture medium, normal fibroblasts are maintained without proliferation, whereas those infected with Rous sarcoma virus proliferate rapidly. This proliferative inactivity of normal fibroblasts does not involve contact-inhibition, since the effect is observed at low, as well as higher, culture densities. When a physiological amount of calcium is added to cultures of normal fibroblasts that have been maintained in very low calcium-plasma medium for 3 days, labeled thymidine uptake and protein synthesis are strongly stimulated, and cell division follows. The use of heat-inactivated chicken serum, instead of plasma, in this medium appears to strongly sensitize normal fibroblasts to the mitogenic action of calcium.

In a plasma-containing culture medium of physiological calcium concentration and a folate concentration of 5 μg/liter, neither normal nor Rous sarcoma virus-infected fibroblasts proliferate to an appreciable extent. The use of serum, however, instead of plasma results in rapid proliferation of both normal and infected cells, as does increase in the folate concentration of the plasma-containing medium to 100 μg/liter.

The fact that while normal fibroblasts are maintained without proliferation in low calcium-plasma medium, Rous sarcoma virus-infected fibroblasts proliferate rapidly, indicates that the effect of calcium is regulatory rather than permissive. These results suggest that the proliferation of normal fibroblasts is initiated by a cellular function involving calcium, and that the autonomous proliferation of the neoplastic fibroblasts results either from increased calcium uptake or from an alteration or a hypass of that function. The results also suggest that serum contains a mitogenic factor(s) not present in plasma, possibly a “wound hormone” for fibroblasts.
Nucleation, Rapid Folding, and Globular Intrachain Regions in Proteins
Authors: Wetlaufer Donald B.
Published: May 2006

Distinct structural regions have been found in several globular proteins composed of single polypeptide chains. The existence of such regions and the continuity of peptide chain within them, coupled with kinetic arguments, suggests that the early stages of three-dimensional structure formation (nucleation) occur independently in separate parts of these molecules. A nucleus can grow rapidly by adding peptide chain segments that are close to the nucleus in aminoacid sequence. Such a process would generate three-dimensional (native) protein structures that contain separate regions of continuous peptide chain. Possible means of testing this hypothesis are discussed.
Nuclear Magnetic Resonance Study of the Thermal Denaturation of Ribonuclease A: Implications for Multistate Behavior at Low pH
Authors: Westmoreland David G. , Matthews C. Robert
Published: May 2006

The thermal denaturation of ribonuclease A has been studied by use of Fourier transform nuclear magnetic resonance by monitoring the imidazole C-2 proton resonances of the histidine residues as a function of temperature at pH 1.3. As the temperature is raised, a slow chemical exchange process results in the disappearance of the peaks corresponding to the native conformation and the appearance of a single peak corresponding to histidine in the denatured state. The disappearance of the native peaks is not simultaneous, implying that at least two regions of the molecule denature at different temperatures. Also, fast chemical exchange processes result in small chemical shifts that appear to be related to local conformational changes. The observed phenomena have been shown to be reversible by the measurement of absorbance at 278 nm, enzyme activity, and nuclear magnetic resonance spectroscopy. The results of this equilibrium study support a multistate denaturation mechanism for ribonuclease A at pH 1.3.
Coagulation of Blood Plasma of Guinea Pig by the Bone Matrix
Authors: Huggins Charles B. , Reddi A. H.
Published: May 2006

Optimal amounts of demineralized bone matrix possess the ability to coagulate platelet-free heparinized, citrated, and oxalated blood plasmas of guinea pigs. Clotting constituents become denatured in contact with the insoluble coagulant proteins. Quantities in excess of optimal modify plasma so that it does not gel when thrombin is added. The newly described coagulant effects are not restricted to the bone matrix, but are present also in the demineralized matrices of tooth and ivory, and in denatured tendon as well. They are regulated properties that were not demonstrated in mineralized bone or native tendon. The coagulant attributes of bone matrix are consistent with those of electropositive polymers of a specific sort.
Concanavalin A Derivatives with Altered Biological Activities
Authors: Gunther Gary R. , Wang John L. , Yahara Ichiro , Cunningham Bruce A. , Edelman Gerald M.
Published: May 2006

Chemical derivatization of tetrameric concanavalin A (Con A) with succinic anhydride or acetic anhydride converts the protein to a dimeric molecule without altering its carbohydrate-binding specificity. At low concentrations, the dose-response curves for the mitogenic stimulation of mouse spleen cells by native Con A and succinyl-Con A are similar. Above lectin concentrations of 10 μg/ml, however, the response to Con A is diminished, while that for succinyl-Con A does not decrease until much higher doses are reached. We have attributed this difference mainly to the higher rate of cell death induced by the native Con A molecule. Con A also shows a greater capacity than succinyl-Con A to agglutinate sheep erythrocytes and to inhibit cap formation by immunoglobulin receptors on spleen cells. Moreover, at low concentrations, Con A induced its glycoprotein receptors to form caps, but succinyl-Con A did not induce cap formation. Addition of antibodies directed against Con A to succinyl-Con A bound on cells restored the properties of agglutination, inhibition of immunoglobulin receptor cap formation, and induction of cap formation by Con A receptors. Similar results have been obtained for acetyl-Con A. These data suggest that the altered biological activities of succinyl-Con A and acetyl-Con A are attributable to their reduced valence.
Nuclear Magnetic Resonance Spectroscopy.
13
C Fourier Transform Spectra of Δ
8
- and Δ
9
-Tetrahydrocannabinol
Authors: Hawkins Bruce L. , Roberts John D.
Published: May 2006

Carbon-13 nuclear magnetic resonance spectra have been taken of Δ
8
- and Δ
9
-tetrahydrocannabinol. The absorptions have been assigned to specific carbons with the aid of off-resonance and selective proton-decoupling experiments, as well as by chemical-shift comparison with model compounds.
Racemization Reaction of Aspartic Acid and Its Use in Dating Fossil Bones
Authors: Bada Jeffrey L. , Protsch Reiner
Published: May 2006

In the time interval datable by radiocarbon, and at the temperatures of most archeological sites, a substantial amount of racemization of aspartic acid takes place. By determination of the amount of racemization of aspartic acid in bones from a particular location which have been dated by the radiocarbon technique, it is possible to calculate the
in situ
first-order rate constant for interconversion of the L- and D enantiomers of aspartic acid. Once this “calibration” has been calculated, the reaction can be used to date other bones from the deposit that are either too old to be dated by radiocarbon or that are too small for radiocarbon dating. The only assumption required with this approach is that the average temperature experienced by the “calibration” sample is representative of the average temperature experienced by older samples. This “calibration” technique is used herein to date bones from the Olduvai Gorge area in Tanzania, Africa.
An Ecological Theory for the Sudden Origin of Multicellular Life in the Late Precambrian
Authors: Stanley Steven M.
Published: May 2006

According to modern ecological theory, high diversity at any trophic level of a community is possible only under the influence of cropping. Until herbivores evolved, single-celled algae of the Precambrain were resource-limited, and a small number of species saturated aquatic environments. In the near-absence of vacant niches, life diversified slowly. Because the changes required to produce the first algae-eating heterotrophs were therefore delayed, the entire system was self-limiting. When the “heterotroph barrier” was finally crossed in the late Precambrian, herbivorous and carnivorous protists arose almost simultaneously, for no major biological differences separate the two groups. These events automatically triggered the formation of a series of self-propagating feedback systems of diversification between adjacent trophic levels. Comparable systems arose among multi-cellular groups, which radiated rapidly from the newly diversifying protist taxa. The sudden proliferation of complex food webs formed by taxa invading previously vacant adaptive zones produced an explosive diversification of life over a period of a few tens of millions of years. The rapid appearance of skeletons in various groups, though of special geological importance, was no more dramatic than other aspects of the radiation. The overall rate of diversification was comparable to rates for less-extensive adaptive radiations of the Phanerozoic.
Different Mechanisms of Energy Coupling for the Active Transport of Proline and Glutamine in
Escherichia coli
Authors: Berger Edward A.
Published: May 2006

The ability of either glucose or D-lactate to energize active transport of amino acids in
E. coli
was studied in starved cells blocked at specific sites of energy metabolism. Proline uptake could be driven by either oxidative or substrate-level processes. The oxidative pathway was sensitive to cyanide but not to arsenate, and operated normally in a mutant deficient in the Ca, Mg-dependent ATPase. The substrate-level pathway, which was active with glucose but not with D-lactate as the carbon source, was sensitive to arsenate but not to cyanide, and required a functional ATPase. Uncouplers prevented the utilization of energy for proline uptake by either pathway.

Energy coupling for glutamine uptake was quite different. The oxidative pathway was sensitive to cyanide and uncouplers and, in contrast with proline, required an active ATPase. The glycolytic component was resistant to cyanide and uncouplers, and functioned normally in the ATPase mutant. Arsenate abolished glutamine transport energized by either pathway.

The results suggest that proline transport is driven directly by an energy-rich membrane state, which can be generated by either electron transport or ATP hydrolysis. Glutamine uptake, on the other hand, is apparently driven directly by phosphate-bond energy formed by way of oxidative or substrate-level phosphorylations.
Attachment of Chloroplast Polysomes to Thylakoid Membranes in
Chlamydomonas reinhardtii
Authors: Chua Nam-Hai , Blobel G. , Siekevitz P. , Palade G. E.
Published: May 2006

Treatment of synchronous cultures of
Chlamydomonas reinhardtii
with chloramphenicol at 4 hr after the beginning of the light phase led to a preferential loss of 70S ribosomes from the 17,000 ×
g
max
supernate. The “lost” 70S ribosomes were found associated with a thylakoid membrane fraction prepared from the 17,000 ×
g
max
pellet. Electron microscopic examinations of this fraction revealed that the 70S ribosomes were bound to the unstacked regions of the thylakoid membranes as polygonal penta- and hexamers. These bound ribosomes were only released by treatment with 500 mM KCl and puromycin, suggesting that both ionic interactions and nascent peptide chains were involved in the ribosome-membrane attachment. Since growth of the thylakoid membranes occurs in the light, it is suggested that bound chloroplast ribosomes function in the synthesis of thylakoid membrane proteins.
The Role of 1
N
6
-Ethenoadenosine Triphosphate and 1
N
6
-Ethenoadenosine Monophosphate in Firefly Luminescence
Authors: Deluca M. , Leonard N. J. , Gates B. J. , McElroy W. D.
Published: May 2006

1,
N
6
-Ethenoadenosine triphosphate (ε-ATP) has been found to be inactive as a substrate for firefly luciferase. However, chemically synthesized luciferyl-εAMP is oxidized by luciferase and light is emitted. The color of the light is red in contrast to the normal yellow-green observed with luciferyladenylate. Although εATP will not serve as a substrate in the activation reaction, the reversal of the activation, pyrophosphorolysis of dehydroluciferyladenylate, will occur with the ethenoadenosine analog.
A Differential Effect of Heavy Water on Temperature-Dependent and Temperature-Compensated Aspects of the Circadian System of
Drosophila pseudoobscura
Authors: Pittendrigh Colin S. , Caldarola Patricia C. , Cosbey Elizabeth S.
Published: May 2006

D
2
O is the only “chemical” agent that consistently affects the frequency of circadian oscillations: its effect is now known to be so widespread and predictable that its action merits closer study as a potential clue to the currently obscure concrete nature of circadian oscillators. The great diversity of D
2
O effects on biological systems in general is briefly reviewed and the need for rejectable hypotheses concerning the action of D
2
O on circadian clocks is stressed because current speculation on its action yields “predictions” expected from almost any hypothesis. We consider the hypothesis that it “diminishes the apparent temperature” of the cell and proceed to test this by examining the effect of D
2
O on temperature-dependent and temperature-compensated aspects of the circadian system in
Drosophila
. We find these components respond as differentially to D
2
O as they do to temperature; we conclude, however, with a warning that this result may be equivocal if, as we now suspect, the frequency of circadian oscillations is generally homeostatically conserved—not only in the face of temperature change, but change in any variable to which it is sensitive. More crucial tests of the temperature-equivalence hypothesis for D
2
O action are defined.
The Defect in the Hunter Syndrome: Deficiency of Sulfoiduronate Sulfatase
Authors: Bach Gideon , Eisenberg Frank , Cantz Michael , Neufeld Elizabeth F.
Published: May 2006

Skin fibroblasts cultured from patients affected with the Hunter syndrome are deficient in the activity of a protein, named the “Hunter corrective factor,” that is required for degradation of dermatan and heparan sulfates. We now show that this factor, purified from human urine, removes about 2% of the sulfate residues from [
35
S]mucopolysaccharide accumulated within Hunter fibroblasts; these groups are derived from “oversulfated” regions of the polymer. Acetone-powder extracts of fibroblasts derived from patients with the Hunter syndrome are deficient in this sulfatase, in contrast to similar extracts from fibroblasts of individuals of other genotype. Hunter corrective factor coupled to α-L-iduronidase (or alternatively, mixed extracts from Hurler and Hunter fibroblasts) release iduronic acid from 4-
O
-α-L-sulfoiduronosyl-D-sulfoanhydromannose. We conclude that the Hunter corrective factor is a sulfatase for sulfated iduronic acid residues.
Regulation of 3-Hydroxy-3-Methylglutaryl Coenzyme A Reductase Activity in Human Fibroblasts by Lipoproteins
Authors: Brown Michael S. , Dana Suzanna E. , Goldstein Joseph L.
Published: May 2006

The activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase (EC 1.1.1.34), the rate-limiting enzyme of hepatic cholesterol biosynthesis, is suppressed in human fibroblasts cultured in the presence of serum. This enzyme activity increases by more than 10-fold after the removal of serum from the medium. The rise in enzyme activity requires
de novo
protein synthesis and is not accompanied by changes in the activities of several other cellular enzymes. The factor responsible for the suppression of 3-hydroxy-3-methylglutaryl coenzyme A reductase activity in cultured fibroblasts is present in the sera of at least four mammalian species, and in human serum it is found in the low-density lipoproteins. Human high-density lipoproteins, very low-density lipoproteins from chicken egg yolk, and the fraction of human serum containing no lipoproteins do not suppress the activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase.
Induction of the Stellate Configuration in Cultured Iris Epithelial Cells by Adenosine and Compounds Related to Adenosine 3′:5′-Cyclic Monophosphate
Authors: Ortiz Jose R. , Yamada Tuneo , Hsie Abraham W.
Published: May 2006

Adenosine, dibutyryl cyclic AMP, monobutyryl cyclic AMP, cyclic AMP, and 5′-AMP have a remarkable morphogenetic effect on cultured iris epithelial cells obtained from adult newt. They alter the broad undulating membrane of the cell into branching strands of cytoplasm, a configuration that has been named “stellate.” Theophylline, a phosphodiesterase inhibitor also induces the stellate configuration. This transient morphological alteration is detectable by 30 min and becomes maximal 80 min after treatment. In the continued presence of the effective compounds the altered cells return to their normal shape, although the recovery period is variable. The morphological alteration of iris epithelial cells
in vitro
observed in the present experiment is reminiscent of that which occurs during the dedifferentiation phase in lens regeneration
in vivo
. These observations suggest that induction of the stellate configuration is relevant to the mechanism of dedifferentiation of newt iris epithelial cells during Wolffian lens regeneration.