bluuebunny/crossref_metadata_2025 huggingface dataset:
Deuterium magnetic resonance studies of the interaction of lipids with membrane proteins.
Authors: Dahlquist F W , Muchmore D C , Davis J H , Bloom M
Published: May 2006

The deuterium magnetic resonance spectra of lipid-protein particles containing cytochrome c oxidase (ferrocytochrome c:oxygen oxidoreductase, EC 1.9.3.1) isolated from beef heart mitochondria and the specifically deuterated lipid 1-(16,16,16-trideuteropalmitoyl)-2-palmitoleoyl phosphatidylcholine are presented. These reconstituted particles are of uniform lipid and protein content; however, the spectra clearly show two environments characterized by distinctly different residual quadrupolar splittings or order parameters. The less-ordered environment shows a splitting similar to but slightly less than that of the pure lipid alone at a given temperature. The more restricted environment appears to be induced by the presence of the protein. The amount of the restricted lipid is clearly temperature dependent with a 2- to 3-fold decrease in relative amount from 2 to 22 degrees. The rate of exchange of lipid between the free and restricted environments is slower than 10(3)/sec. The significance of these phenomena is discussed.
Reversible and irreversible inhibition by anesthetics of the calcium-induced luminescence of aequorin.
Authors: Kamaya H , Ueda I , Eyring H
Published: May 2006

The actions of various kinds of so-called membrane-stabilizing drugs on Ca2+-induced flash intensity of purified aequorin, a photoprotein obtained from Aequorea aequorea, were examined. All drugs used in this experiment, including inhalational anesthetics, tetracaine, chlorpromazine, and morphine, depressed flash intensity, and the inhibition increased with time. The inhibition followed a mixture of reversible and irreversible kinetics. A method of analyzing irreversible kinetics is presented. The dissociation constants for reversible inhibition and the rate constants for irreversible inhibition are presented for each agent.
Contrast variation study of specifically deuterated Escherichia coli ribosomal subunits.
Authors: Crichton R R , Engleman D M , Haas J , Koch M H , Moore P B , Parfait R , Stuhrmann H B
Published: May 2006

A neutron small-angle scattering analysis has been done on partially deuterated 30S and 50S subunits of Escherichia coli ribosomes by the contrast variation method. The results indicate that the central regions of both particles are RNA-rich whereas their exteriors are protein-rich. The segregation of RNA and protein is much greater in the 50S subunit than in the 30S; the 30S subunit approaches a homogeneous mixture of RNA and protein. In both structures the most probable separation between the centers of mass of their protein and RNA distributions is small, although substantial variation of this parameter is possible within experimental error.
Molecular basis of reovirus virulence: Role of the S1 gene
Authors: Weiner Howard L. , Drayna Dennis , Averill Damon R. , Fields Bernard N.
Published: May 2006

A genetic approach has been used to define the molecular basis for the different patterns of virulence and central nervous system cell tropism exhibited by reovirus types 1 and 3. Intracerebral inoculation of reovirus type 3 into newborn mice causes a necrotizing encephalitis (without ependymal damage) that is uniformly fatal. Animal inoculated with reovirus type 1 generally survive and may develop epedymal cell damage (without neuronal necrosis) and hydrocephalus. Using recombinant clones derived from crosses between reovirus types 1 and 3, we have been able to determine that the S1 genome segment is responsible for the differing cell tropism of reovirus serotypes and is the major determinant of neurovirulence. The type 1 S1 genome segment is responsible for ependymal damage with subsequent hydrocephalus; the type 3 S1 genome segment is responsible for neuronal necrosis and neurovirulence. We postulate that these differences are due to the specific interaction of the σ1 outer capsid polypeptide (the protein coded for by the S1 genome segment) with receptors on the surface of either ependymal cells or neuronal cells.
Determination of transmitter function by neuronal activity
Authors: Walicke Patricia A. , Campenot Robert B. , Patterson Paul H.
Published: May 2006

The role of neuronal activity in the determination of transmitter function was studied in cultures of dissociated sympathetic neurons from newborn rat superior cervical ganglia. Cholinergic and adrenergic differentiation were assayed by incubating the cultures with radioactive choline and tyrosine and determining the rate of synthesis and accumulation of labelled acetylcholine and catecholamines. As in previous studies, pure neuronal cultures grown in control medium displayed much lower ratios of acetylcholine synthesis to catecholamine synthesis than did sister cultures grown in medium previously conditioned by incubation on appropriate nonneuronal cells (conditioned medium). However, here we report that neurons treated with the depolarizing agents elevated K
+
or veratridine, or stimulated directly with electrical current, either before or during application of conditioned medium, displayed up to 300-fold lower acetylcholine/catecholamine ratios than they would have without depolarization, and thus remained primarily adrenergic. Elevated K
+
and veratridine produced this effect on cholinergic differentiation without significantly altering neuronal survival. Because depolarization causes Ca
2+
entry in a number of cell types, the effects of several Ca
2+
agonists and antagonists were investigated. In the presence of the Ca
2+
antagonists D600 or Mg
2+
, K
+
did not prevent the induction of cholinergic properties by conditioned medium. Thus depolarization, either steady or accompanying activity, is one of the factors determining whether cultured sympathetic neurons become adrenergic or cholinergic, and this effect may be mediated by Ca
2+
.
The number of receptors for beta-melanocyte stimulating hormone in Cloudman melanoma cells is increased by dibutyryl adenosine 3':5'-cyclic monophosphate or cholera toxin.
Authors: DiPasquale A , McGuire J , Varga J M
Published: May 2006

Cultured Cloudman melanoma cells exposed either to dibutyryl 3':5'-cyclic AMP and theophylline or to cholera toxin bind significantly more 125I-labeled beta-melanocyte stimulating hormone (MSH) and fluorescein-labeled MSH than untreated cells. MSH binds to melanoma cells in the G2 phase of the cell cycle. The stimulation of MSH binding by dibutyryl cyclic AMP results from an increase in the number of MSH receptors per G2 cell and, to a lesser extent, from an increase in the number of G2 cells. The affinity of the receptors for MSH is not influenced by dibutyryl cyclic AMP.
Dissociation of increases in levels of 3':5'-cyclic AMP and 3':5'-cyclic GMP from induction of ornithine decarboxylase by the tumor promoter 12-O-tetradecanoyl phorbol-13-acetate in mouse epidermis in vivo.
Authors: Mufson R A , Astrup E G , Simsiman R C , Boutwell R K
Published: May 2006

A single application of 17 nmol of 12-O-tetradecanoyl phorbol-13-acetate (TPA) to mouse skin caused a marked (200- to 400-fold) induction of ornithine decarboxylase (EC 4.1.1.17, L-ornithine carboxy-lyase) activity in mouse epidermal and epidermal-dermal preparations. No change in the basal level of 3':5'-cyclic AMP occurred in epidermal-dermal preparations within 30 min of TPA application. Intraperitoneal injection of the beta-agonist isoproterenol resulted in a dose-dependent accumulation of 3':5'-cyclic AMP occurred in epidermal-dermal preparations within 30 min of TPA application. Intraperitoneal injection of the beta-agonist isoproterenol resulted in a dose-dependent accumulation of 3':5'-cyclic AMP 10 min after injection, but caused no induction of ornithine decarboxylase. When isoproterenol was injected 10 min prior to an application of either 1.7 or 17 nmol of TPA, the magnitude of the ornithine decarboxylase induction was the same as induction with TPA alone. Topical application of 17 nmol of TPA caused no increase in the level of 3':5'-cyclic GMP present in the mouse epidermal-dermal preparations 2-20 min after application. Intraperitoneal injection of 1.75 mumol of dibutyryl 3':5'-cyclic GMP and/or butyryl derivatives of cyclic GMP caused a 6-fold increase in the level of cyclic GMP and/or butyryl derivatives of cyclic GMP in epidermal-dermal preparations within 5 min of injection, and the level remained elevated for at least 20-30 min. This dose of dibutyryl 3':5'-cyclic GMP was incapable of inducing ornithine decarboxylase. Injection of dibutyryl 3':5'-cyclic GMP 5 min before application of 1.7 nmol of TPA or 30 min before application of 17 nmol of TPA did not alter the magnitude of the ornithine decarboxylase induction produced by TPA alone. These results suggest that early increases in the total intracellular levels of either 3':5'-cyclic AMP or 3':5'-cyclic GMP are not part of the mechanism by which TPA induces ornithine decarboxylase in the epidermis.
Microcomplement fixation studies on the evolution of alpha-glycerophosphate dehydrogenase within the genus Drosophila.
Authors: Collier G E , MacIntyre R J
Published: May 2006

Antisera were prepared against purified alpha-glycerophosphate dehydrogenase (EC 1.1.1.8) (alphaGPDH) from Drosophila melanogaster, D. virilis, and D. busckii. The immunological distances between the enzymes from the 3 species and those from 31 additional drosophilid species agree in general with the accepted phylogeny of the genus. These data permit an estimate that the subgenus Sophophora diverged 52 million years ago from the line leading to the subgenus Drosophila. The antiserum against melanogaster alphaGPDH was capable of distinguishing allelic variants of alphaGPDH. On the basis of presumed single amino acid substitutions, no drosophilid alphaGPDH tested differed from the melanogaster enzyme by more than eight or nine substitutions. The study was extended to include representatives of six other dipteran families. The immunological distances between alphaGPDH from Drosophila and alphaGPDH from these dipterans were reasonably consistent with a phylogeny of the order Diptera established by more conventional means. The unit evolutionary period of this enzyme was estimated to be 18 million years.
A new class of murine leukemia virus associated with development of spontaneous lymphomas.
Authors: Hartley J W , Wolford N K , Old L J , Rowe W P
Published: May 2006

A new type of murine leukemia virus has been detected in thymuses of leukemic and late preleukemic AKR mice, in lymphomas developing in NIH Swiss mice carrying the AKR ectopic virus-inducing loci Akv-I or Akv-2, and in the thymus of a preleukemic C58 mouse. The viruses induce focal areas of morphologic alteration in a mink lung cell line and are tentatively referred to as "mink cell focus-inducing" (MCF) strains. They have the host range of both xenotropic and N-tropic ecotropic murine leukemia viruses, are neutralized by antisera to both ecotropic and xenotropic viruses, and are interfered with by both viruses. They may represent a particular type of genetic recombinant which emerges during the preleukemic period in high-ecotropic-virus mouse strains, and they may play a significant role in the etiology of spontaneous lymphomas.
Evidence for active role of cilia in sensory transduction.
Authors: Moran D T , Varela F J , Rowley J C
Published: May 2006

Combined high-voltage electron-microscopic and electrophysiological studies strongly suggest that cilia play an active role in sensory transduction in the grasshopper proximal femoral chordotonal organ (FCO) a ciliated mechanoreceptor. The FCO of pro- and mesothoracic legs of Melanoplus bivittatus contains a group of several hundred chorodontal sensilla arranged in a near-parallel bundle and slung between the proximal femur and the knee joint. Both flexion and extension of the tibia stimulate the FCO, which appears to measure the femoro-tibial angle. The FCO's U-shaped response curve indicates that progressive flexion or extension from the resting joint angle of 90 degrees increases the response frequency of individual receptors and recruits additional units as well. Since the FCO is a purely tonic mechanoreceptor, it is possible to fix FCOs during maximum and minimum states of stimulation and electron-microscopically observed changes in the receptor's fine structure. The most conspicuous change is the production of a pronounced bend at the base of the sensory cilia in chordotonal sensilla of maximally stimulated femoral chordotonal organs.
Catecholamine hormone receptor differences identified on 3T3 and simian virus-transformed 3T3 cells.
Authors: Sheppard J R
Published: May 2006

Identification and characterization of hormone receptors on the cell surface is an effective tool for studying the plasma membrane. Using the direct binding of a radiolabeled antagonist, (-)[3H]alprenolol, to crude membrane preparations, and a physiological response (cellular cyclic AMP levels), I demonstrated a catecholamine (beta-adrenergic) hormone receptor site coupled to a catecholamine responsive adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] on 3T3 and simian virus 40 (SV40)-transformed 3T3 cells. At a concentration of 1 muM, epinephrine and isoproterenol elevate cellular cyclic AMP levels 8- and 12-fold, respectively, in both cell lines. Norepinephrine was also a potent agonist on 3T3 cells (8-fold stimulation), but SV3T3 cells showed a lesser (2-fold) response to this hormone. The specificity of the physiological response (as well as the direct binding studies using the alprenolol radiolabel) is indicated by the increased effectiveness of (-) compared to (+) stereoisomers, rapid and reversible kinetics (steady state within 2 min), high affinity (Kd approximately 30 nM) and saturability (indicating a finite number of hormone receptors). These hormone receptor studies indicate the 3T3 cells have a beta1 adrenergic receptor while the SV3T3 cells have a receptor with beta2 qualities. In addition, the number of beta-adrenergic hormone receptors appear to be increased in the normal 3T3 cells by approximately 2-fold over the SV3T3 cells (300 versus versus 120 femtomol/mg of protein).
Levels of delta-aminolevulinate dehydratase, uroporphyrinogen-I synthase, and protoporphyrin IX in erythrocytes from anemic mutant mice.
Authors: Sassa S , Bernstein S E
Published: May 2006

Levels of erythrocyte delta-aminolevulinate dehydratase [ALA-dehydratase; porphobilinogen synthase; 5-aminolevulinate hydro-lyase (adding 5-aminolevulinate and cyclizing), EC 4.2.1.24], UROPORPHYRINOGEN-I synthase [Uro-synthase; porphobilinogen ammonia-lyase (polymerizing), EC 4.3;1.8], AND PROTOPORPHYRIN IX (Proto) were measured by sensitive semimicroassays using 2-5 mul of whole blood obtained from normal and anemic mutant mice. The levels of erythrocyte ALA-dehydratase and Uro-synthase showed marked developmental changes and ALA-dehydratase was influenced by the Lv gene. Mice with overt hemolytic diseases (ja/ja, sph/sph, nb/nb, ha/ha) had 10- to 20-fold increases in ALA-dehydratase, Uro-synthase, and Proto compared with their normal controls. Mice with an iron deficiency (mk/mk) and mice with hypoplastic anemias (W/Wv, Sl/Sld, an/an) had mild to moderate increases in these parameters. Elevated enzyme activities and Proto correlated well with the number of reticulocytes. Because all mice with anemias possessed elevated levels of ALA-dehydratase, Uro-synthase, and Proto independent of differences in their genotypes, the increase in these parameters is not likely to be the result of a specific gene defect. The increased enzyme activities and Proto concentration probably reflect increased frequency of young red cells that are still active in heme biosynthesis.
Specific receptor sites for chemotactic peptides on human polymorphonuclear leukocytes.
Authors: Williams L T , Snyderman R , Pike M C , Lefkowitz R J
Published: May 2006

Synthetic N-formylmethionyl peptides are chemotactic attractants for human polymorphonuclear leukocytes. The well-defined structure-activity relationship of these peptides in eliciting a chemotactic response suggests that the interaction of the peptides with a specific cellular binding site may initiate chemotaxis. By using tritiated N-formylmethionyl-leucyl-phenylalanine (fMet-Leu-[3H]Phe), a potent chemotactic peptide with high specific radioactivity, we have directly identified binding sites on human polymorphonuclear leukocytes. Binding of fMet-Leu-[3H]Phe to polymorphonuclear leukocytes is rapid (t1/2 less than 2 min) and reversible. The equilibrium dissociation constant (KD) for the interaction of fMet-Leu-[3H-A1Phe with the binding site is 12-14 nM at 37 degrees. The number of binding sites is approximately 2000 per cell. The specificity of the binding sites for a series of N-formylmethionyl peptides exactly reflects the specificity of the chemotactic response to the peptides in that they compete for the binding sites and initiate chemotaxis with the same order of potency (fMet-Leu-Phe greater than fMet-Met-Met greater than fMet-Phe greater than fMet-Leu greater than fMet),fPhe-Met is a competitive antagonist of the chemotactic activity of N-formylmethionyl peptides and has a calculated KD of 6x10-5 M. FPhe-Met also half-maximally inhibits binding of fMet-Leu[3H]Phe binding was the highest in polymorphonuclear leukocytes. No binding of fMet-Leu-[3H]Phe to human erythrocytes could be detected. These data indicate that fMet-Leu-[3H]Phe can be used to identify binding sites for chemotactic peptides on human polymorphonuclear leukocytes. It is likely that these binding sites initiate the specific response of motile cells to N-formylmethionyl peptides.
Multispecific lymphoid cell surface receptors.
Authors: Czaja M J , Richards F F , Varga J M
Published: May 2006

When mice are sequentially immunized with two antigens to give an oligoclonal "double-binding" antibody response, there is a concomitant increase of "double-binding" cell surface receptors on their splenic lymphocytes. Competition studies suggest that the capacity to bind the two ligands, bovine pancreatic ribonuclease (EC 3.1.4.22) and a 2,4-dinitrophenyl (DNP) derivative, is a function of the same molecules. In ribo-nuclease-primed mice, an early response to bovine gamma globulin containing an average of 60 Dnp groups per molecule is the appearance of an increasing number of cells bearing surface receptors binding both ribonuclease and Dnp. Later, these double-binding cells are diluted by cells that bind Dnp, but not ribonuclease. The analogous phenomenon is observed when the two antigens are used in reverse order. While other reports suggest that there may be several different receptors in relatively undifferentiated cells from unimmunized mice, it seems likely that cells committed to antibody production carry a predominant multispecific cell surface immunoglobulin receptor.
Analysis of human Y-chromosome-specific reiterated DNA in chromosome variants.
Authors: Kunkel L M , Smith K D , Boyer S H , Borgaonkar D S , Wachtel S S , Miller O J , Breg W R , Jones H W , Rary J M
Published: May 2006

A number of individuals with aberrant Y chromosomes have been tested for the presence of Y-chromosome-specific reiterated DNA. These studies locate Y-chromosome-specific reiterated sequences on the long arm of the Y chromosome. Correlation with phenotype and other known Y chromosome markers establish that the Y-chromosome-specific reiterated DNA discussed here has no evident role in male determination.
Ethylphenacemide and phenacemide: conformational similarities to diphenylhydantoin and stereochemical basis of anticonvulsant activity.
Authors: Camerman A , Camerman N
Published: May 2006

The three-dimensional molecular structures of the potent anticonvulsant agents phenacemide and ethylphenacemide have been determined by single-crystal x-ray diffraction. Although these compounds possess straight-chain acetylurea groupings, in the crystalline state both molecules adopt a pseudocyclic conformation of the acetylurea chain through amide...carbonyl oxygen intramolecular hydrogen bonding. This results in spatial positioning and relative orientation of two electron-donating functional groups in these molecules similar to those of comparable atoms in diphenylhydantoin and other heterocycle-containing anticonvulsants.
Mutual entrainment of bilaterally distributed circadian pacemaker.
Authors: Page T L , Caldarola P C , Pittendrigh C S
Published: May 2006

The interactions between the bilaterally distributed components of the circadin system that controls the locomotor activity rhythm of the cockroach Leucophaea maderae were investigated in a series of surgical lesion experiments. Complete excision of one optic lobe (either right or left) or its surgical isolation from the central nervous system had no effect on the animals' ability to free-run in constant darkness nor was there any indication, as judged by postoperative pi values of any difference between left and right lobe pacemakers. However, these surgical procedures consistently resulted in a significant increase in tau over preoperative value while optic nerve section had no effect on tau. The propostion is developed that the left and right pacemakers in the two optic lobes are mutally coupled and that the compound pacemaker's period is shorter than either of its constituent pacemakers. It was also found that the integrity of either compound eye is sufficient to assure entrainment of both left and right pacemakers.
Explicit Plancherel theorem for ground state representation of the Heisenberg chain
Authors: Babbitt Donald G. , Thomas Lawrence E.
Published: May 2006

In its ground state representation, the infinite spin 1/2 Heisenberg chain provides a model for spin wave scattering that entails many features of the quantum mechanical
N
-body problem. Here, we give a complete eigenfunction expansion for the Hamiltonian of the chain in this representation, for
all
numbers of spin waves. Our results resolve the questions of completeness and orthogonality of the eigenfunctions given by Bethe for finite chains, in the infinite volume limit.
Embryonic chicken brain and mouse neuroblastoma cells N1E-115 and N-18 contain an inhibitor of acid deoxyribonuclease.
Authors: Bhattacharya P , Moskal J R , Basu S
Published: May 2006

Activity of a trypsin-sensitive acid deoxyribonuclease (DNase) inhibitor has been detected in 13- to 21-day-old embryonic chicken brains and in clonal lines of neuroblastoma cells (adrenergic, N1E-115, and neurotransmitter-inactive, N-18) grown for 48 hr after subculture. The activities of purified porcine and bovine spleen DNases were inhibited 60--75% in the presence of the inhibitor, whereas less than 10% inhibition was observed with purified pancreatic DNase. Activities of an acidic DNase and its inhibitor reached maxima in 21-day-old embryonic chicken brain. The proteins were separated by isoelectric focusing and affinity column chromatographic techniques. The pI values of the acid DNase and its inhibitor were 5.4 and 4.2, respectively.
Tryptic peptide analysis of normal and mutant forms of hypoxanthine phosphoribosyltransferase from HeLa cells.
Authors: Milman G , Krauss S W , Olsen A S
Published: May 2006

Hypoxanthine phosphoribosyltransferase (HPRT, IMP:pyrophosphate phosphoribosyltransferase, EC 2.4.2.8) can be purified 5-to 10,000-fold from extracts of HeLa (human) cells by a three-step procedure consisting of high-speed centrifugation, adsorption to Sepharose-conjugated HPRT antibody, and sodium dodecyl sulfate/polyacrylamide gel electrophoresis. Purified enzyme labeled in vivo with radioactive lysine, arginine, or methionine was digested with trypsin and the tryptic peptides were separated by column chromatography on Bio-Rad cation exchanger Aminex A-5. Less than 50 ng (2 pmol) of HPRT is required to produce a tryptic peptide pattern. A methionine-labeled peptide was identified as the COOH-terminus because it was not labeled with either lysine or arginine. We have compared the tryptic peptide patterns of normal HeLaHPRT and a crossreacting HPRT protein lacking enzyme activity from HeLa mutant H23 [Milman et al. (1976) Proc. Natl. Acad. Sci. USA 73, 4589--4593]. The mutant protein has a new lysine-labeled peptide, but the chromatography patterns of arginine- or methionine-labeled peptides appear identical to those of the normal protein. The appearance in the H23 mutant HPRT protein of a new tryptic peptide provides strong evidence for a mutation in the HPRT structural gene. The tryptic peptide patterns were used to determine the total number of residues of labeled amino acid in the protein, and the values are reasonably consistent with those determined by conventional amino acid analysis pf erythrocyte HPRT.
Effect of batrachotoxin on the electroplax of electric eel: evidence for voltage-dependent interaction with sodium channels.
Authors: Bartels-Bernal E , Rosenberry T L , Daly J W
Published: May 2006

Batrachotoxin under certain conditions has a strong depolarizing effect on the innervated membrane of the monocellular electroplax preparation from the electric eel, El-ectrophorus electricus. No effect is observed when the toxin (50-200 nM) is applied to the resting membrane for periods up to 1 hr. However, if the membrane is exposed to batrachotoxin and the cell is subjected to stimulation at a stimulus voltage slightly above the threshold for action potential firing, a progressive prolongation of the action potential and concomitant progressive depolarization of the innervated membrane is observed. When the membrane is depolarized by 15-20 mV, a further abrupt all-or-none depolarization occurs, and the potential attains a steady-state value between 0 and -10 mV. Brief stimulation of a cell in the presence of batrachotoxin is sufficient to define a batrachotoxin-treated cell, even though negligible depolarization occurs. If depolarizing agents such as carbamoylcholine or potassium chloride are introduced to such a cell in concentrations that normally produce a 20-30 mV depolarization, the abrupt all-or-none depolarization immediately occurs. All-or-none depolarizations arising from either electrical stimulation or depolarizing agents are unaffected by d-tubocurarine but are completely reversed by tetrodotoxin. Batrachotoxin thus appears to activate only the action potential sodium channels. In the batrachotoxin-treated membrane, these channels can attain stable steady states in either a closed configuration at the normal resting potential or in an open configuration after complete depolarization. A striking hysteresis cycle thus can be generated, which is strongly indicative of a voltage-dependent interaction of the toxin with the action potential sodium channels.
Cauchy integrals on Lipschitz curves and related operators
Authors: Calderón A. P.
Published: May 2006

In this note, we establish certain properties of the Cauchy integral on Lipschitz curves and prove the

L
p

-boundedness of some related operators. In particular, we obtain the recent results of R. R. Coifman and Y. Meyer [(1976) “Commutateurs d'intégrales singulières:”
Analyse harmonique d'Orsay
n
o
211, Université Paris XI] on the continuity of the so-called commutator operators.
Association of a protein structure of probable membrane derivation with HeLa cell mitochondrial DNA near its origin of replication.
Authors: Albring M , Griffith J , Attardi G
Published: May 2006

Almost all (about 95%) of the mitochondrial DNA molecules released by Triton X-100 lysis of HeLa cell mitochondria in the presence of 0.15 M salt are associated with a single protein-containing structure varying in appearance between a 10-20 nm knob and a 100-500 nm membrane-like patch. Analysis by high resolution electron microscopy and by polyacrylamide gel electrophoresis after cleavage of mitochondrial DNA with the endonucleases EcoRI, HindIII, and Hpa II has shown that the protein structure is attached to the DNA in the region of the D-loop, and probably near the origin of mitochondrial DNA replication. The data strongly suggest that HeLa cell mitochondrial DNA is attached in vivo to the inner mitochondrial membrane at or near the origin of replication, and that a membrane fragment of variable size remains associated with the DNA during the isolation. After sodium dodecyl sulfate extraction of mitochondrial DNA, a small 5-10 nm protein is found at the same site on a fraction of the mitochondrial DNA molecules.
Nucleotide sequence at the 5' terminus of the avian sarcoma virus genome.
Authors: Shine J , Czernilofsky A P , Friedrich R , Bishop J M , Goodman H M
Published: May 2006

Transcription of DNA from the RNA genome of avian sarcoma virus by RNA-directed DNA polymerase in vitro initiates on a primer (tRNATrp) located near the 5'-terminus of the viral genome. One of the major products of transcription is a single-stranded DNA chain complementary to a sequence of 101 nucleotides immediately distal to the site of initiation of DNA synthesis. We have determined the complete nucleotide sequence of this transcribed chain for the Prague strain of avian sarcoma virus, a partial sequence of the transcribed chain for the Bratislava 77 strain of avian sarcoma virus, and the sequence of a DNA transcript that is shorter than the transcribed single-stranded chain. Our data define the location of tRNATrp on the genome of avian sarcoma virus and provide the sequence of 119 nucleotides at the 5'-terminus of the genome. Portions of this sequence may be involved in the binding of RNA-directed DNA polymerase, the initiation of translation from viral messenger RNA, the extension of RNA-directed DNA synthesis from the 5'- to the 3'-terminus of viral RNA, and the integration of viral DNA into the host genome.
Partial amino acid sequence of two major component polypeptides of hepatitis B surface antigen.
Authors: Peterson D L , Roberts I M , Vyas G N
Published: May 2006

Determination of the amino acid sequence of the immunogenic polypeptides of hepatitis B surface antigen may not only permit molecular localization of the distinct determinants a, d, and y but may also lead to the synthesis of a hapten useful in prophylactic immunization against hepatitis B virus infection. For this purpose, purified monotypic hepatitis B surface antigen of adw subtype was resolved into equal amounts of two major polypeptides (22,000 and 28,000 daltons) and up to six other minor polypeptides by polyacrylamide gel electrophoresis. With the periodate staining reaction, only the 28,000-dalton polypeptide stained as a glycoprotein. Guinea pigs immunized with the 22,000-dalton polypeptide produced potent antisera against determinants a and d, but the 28,000-dalton glycoprotein did not induce a response. Both polypeptides isolated by preparative polyacrylamide gel electrophoresis showed amino acid composition identical with that of the intact antigen. For both polypeptides, hydrazinolysis gave Ile as the carboxyterminus, and carboxypeptidase A digestion gave the same terminal sequence, Val-Tyr-Ile. Both peptides also yielded an identical sequence of amino acids in nine steps of Edman degradation--Met-Glu-Asn-Ile-Thr-Ser(Cys)-Gly-Phe-Leu. Our data suggest that hepatitis B surface antigen contains a single major immunogenic 22,000-dalton polypeptide component, part of which is modified by the addition of carbohydrate to give rise to the glycopeptide of apparent molecular weight 28,000.
Microinjection analysis of envelope-glycoprotein messenger activities of avian leukosis viral RNAs.
Authors: Stacey D W , Allfrey V G , Hanafusa H
Published: May 2006

Virion RNA from the avian leukosis virus Rous-associated virus 2 (RAV-2) and poly(A)-containing RNAs from RAV-2-infected chick embryo fibroblasts were microinjected into fibroblasts transformed by the Bryan high-titer strain of Rous sarcoma virus (RSV), which is deficient in viral envelope glycoprotein. Production of infectious RSV following these injections depended upon the viral envelope-messenger activity of the injected RNA. This system constituted a sensitive and rigorous assay system for viral envelope-messenger RNA. It was found that 21S mRNA from RAV-2-infected cells expressed the highest activity, while 35S mRNA expressed comparatively little. In addition, RAV-2-virion RNA expressed little messenger activity. The rate of formation of infectious RSV following 21S mRNA injections reached a peak near 9 hr, which was followed by a rapid decline. Evidence has been obtained that a small fraction of both 35S virion RNA and 35S mRNA from virus-infected cells was encapsulated into virus particles following their injection into virus-producing cells.
Application of imidazole as a selective inhibitor thromboxane synthetase in human platelets.
Authors: Needleman P , Raz A , Ferrendelli J A , Minkes M
Published: May 2006

Human platelet suspensions release a rabbit-aorta-contracting substance (previously identified as thromboxane A2) during aggregation produced by arachidonic acid, prostaglandin endoperoxide, thrombin, and collagen. Incubation of platelets with imidazole did not interfere with the aggregation produced by these agonists but markedly reduced the generation of the rabbit-aorta-contracting substance. We find that imidazole inhibited the conversion of exogenous or endogenous prostaglandin endoperoxide into thromboxane A2-Imidazole selectively inhibits thromboxane synthetase in intact human platelets, because this agent blocks the conversion of [14C]arachidonate into [14C]thromboxane B2 but does not inhibit the conversion of [14C]arachidonate into [14C]prostaglandin E2. The inhibition of thromboxane synthetase by imidazole is not the result of an alteration in platelet 3':5'-cyclic AMP levels. These results illustrate the utility of imidazole as a pharmacological tool and demonstrate the two unique and dissociable properties of the endoperoxides themselves--their ability to aggregate platelets and their enzymatic conversion to the potent vasoconstrictor thromboxane.
Absorbing boundary conditions for numerical simulation of waves
Authors: Engquist Björn , Majda Andrew
Published: May 2006

In practical calculations, it is often essential to introduce artificial boundaries to limit the area of computation. Here we develop a systematic method for obtaining a hierarchy of local boundary conditions at these artifical boundaries. These boundary conditions not only guarantee stable difference approximations, but also minimize the (unphysical) artificial reflections that occur at the boundaries.
Microenvironment of the binding site in the lac carrier protein.
Authors: Schuldiner S , Weil R , Robertson D E , Kaback H R
Published: May 2006

Studies with a homologous series of (N-dansyl)aminoalkyl-1-thio-beta-D-galactopyranosides containing two to six methylene carbons bridging the galactosyl and dansyl ends of the molecules are described. The compounds were utilized in radioactive and nonradioactive form, and binding of each homologue to membrane vesicles isolated from Escherichia coli ML 308-225 was measured directly by flow dialysis in the presence of D-lactate. The results are compared with the D-lactate-induced fluorescence enhancement observed with each dansylgalactoside and with the ability of N-methylpicolinium perchlorate to quench the fluorescence of the bound homologues. The binding affinity of the lac carrier protein for the probes varies directly with the length of the alkyl linkage, and the same number of binding sites is observed with each homologue. In contrast, however, the increase in fluorescence observed upon binding varies dramatically as the alkyl chain is increased in length, with the fluorescence exhibiting maximal values at two and six methylene carbons and a minimum at four methylene carbons. Furthermore, quenching by N-methylpicolinium perchlorate exhibits an inverse relationship and maximum quenching is observed with the 4 carbon homologue. Possible reasons for this behavior are discussed.
Aminoacyl-tRNA binding at the recognition site is the first step of the elongation cycle of protein synthesis.
Authors: Lake J A
Published: May 2006

Codon recognition occurs during protein synthesis with the aminoacyl-tRNA bound in the recognition (or R) tRNA-binding site. The recognition site is thought to be located on the external surface of the smaller ribosomal subunit distal from the interface between subunits, where the aminoacyl (A) and peptidyl (P) tRNA-binding sites are located. A molecular model describing the switching of the aminoacyl-tRNA from the R site to the A site is proposed. Details of the model include codon recognition at the R site by an aminoacyl-tRNA with its anticodon loop in the 5' stacked conformation; movement of the aminoacyl-tRNA from the R site to the A site by a switching in the anticodon loop from the 5' stacked conformation to the 3' stacked conformation; and recognition of the correct reading frame by a base-pairing interaction between the A and P site tRNAs that involves trans pairing of the invariant bases U-33 of both molecules.
Do myoblasts in vivo withdraw from the cell cycle? A reexamination.
Authors: Buckley P A , Konigsberg I R
Published: May 2006

The proliferative fraction of mononucleated cells in differentiating chick embryonic wing muscle (day 11) was measured following continuous infusion of tritiated thymidine into the embryonic circulation. During progressively longer intervals of infusion of the isotopically labeled precursor, the percentage of cells that enter S becomes larger, reaching 92% at the longest time period measured (21 hr). These observations suggest that until they are withdrawn into nonreplicative muscle syncytia, virtually all of the single cells in differentiating embryonic muscle remain in the proliferative pool. Earlier calculations of the size of this pool in developing muscle, based on the percentage of cells in S during a brief pulse, indicated, however, that less than half of the mononucleated cells are still replicating. We therefore compared the size of the proliferative fraction determined by continuous labeling with the calculation of this same parameter using our own pulse-labeling data. We find that the calculation underestimates the size of the proliferative pool and is, in fact, an estimate of only that portion of the cells whose generation times cluster around the average. This underestimate is particularly pronounced in differentiating muscle in which, concomitant with myogenic fusion, the distribution of G1 times (and consequently generation times as well) becomes longer and more highly variable. Our results suggest that the mode of administering the labeled DNA precursor profoundly affects the measurement of cell cycle parameters in vivo when these parameters exhibit considerable variability. The data presented here do not support the notion that any sizeable fraction of the myoblast population is withdrawn from the cell cycle for any significant period of time prior to fusion.
Genetic mapping of Rhizobium meliloti.
Authors: Meade H M , Signer E R
Published: May 2006

The drug resistance factor RP4, originally isolated in Pseudomonas, was transferred to Rhizobium meliloti. In that strain, RP4 promotes conjugational transfer of chromosomal markers to form haploid recombinants. This mating system has been used to construct a linkage map of R. meliloti.
Accelerated degradation of acetylcholine receptor from cultured rat myotubes with myasthenia gravis sera and globulins.
Authors: Appel S H , Anwyl R , McAdams M W , Elias S
Published: May 2006

Altered geometry of the neuromuscular junction and a decreased number of acetylcholine receptors appear responsible for the defect of neuromuscular transmission in myasthenia gravis. We have used cultured rat myotubes as a model to study in vitro the potential role of myasthenic globulins in the pathological process. Acetylcholine receptor content was assayed by the extent of 125I-labeled alpha-bungarotoxin binding, and acetylcholine receptor function was assayed by the sensitivity to acetylcholine iontophoresis. The half-life of the acetylcholine receptor was 18.5 hr in the presence or absence of control sera. Myasthenic sera and globulins produced a gradual reduction in acetylcholine receptors, as assessed by biochemical and electrophysiological techniques. The half-life in the presence of myasthenic sera was 6 hr. The accelerated turnover was unaffected by puromycin but was slowed by lowered temperature (18-20 degrees), interference with energy metabolism (2,4-dinitrophenol), and interference with cytoskeletal structures (colchicine and cytochalasin B). We found no electrophysiological evidence to suggest globulin blockade of acetylcholine access to the acetylcholine receptor. Our observations suggest that circulating globulins in myasthenia gravis may contribute to the functional defects of neuromuscular transmission by accelerating the rate of internationalization and degradation of surface membrane acetylcholine receptors.
Inhibition by anti-interferon serum of lymphocytic choriomeningitis virus disease in suckling mice.
Authors: Rivière Y , Gresser I , Guillon J C , Tovey M G
Published: May 2006

Inoculation of newborn mice with lymphocytic chloriomeningitis (LCM) virus resulted in decreased weight gain, liver cell necrosis, and death. Injection of potent sheep immunoglobulin against mouse interferon markedly inhibited these manifestations of LCM virus disease despite the fact that these treated mice had 100-fold more LCM virus in their serum. We conclude that interferon induced by LCM virus is responsible in large part for the syndrome of growth inhibition, liver cell necrosis, and death observed in LCM virus-infected suckling mice.
Pancreatic immunoreactive somatostatin release.
Authors: Patton G S , Ipp E , Dobbs R E , Orci L , Vale W , Unger R H
Published: May 2006

The location of the somatostatin-containing D-cells of the pancreatic islets between the A- and B-cells suggests that their function might be to inhibit insulin and/or glucagon secretion by these neighboring cells. To determine if insulin and/or glucagon, in concentrations that might be present in the extracellular space surrounding the D-cells, stimulate immunoreactive somatostatin (IRS) release, we perfused 10 microng of glucagon or 10 milliunits of insulin per ml in 11 isolated dog pancreases, for 40 min in seven experiments and for 100 min in four experiments. In eight of the nine experiments in which glucagon was perfused, a prompt and significant rise in mean IRS release, ranging from 71 to 128% above the control level, was observed. In the eight experiments in which insulin was perfused. IRS did not increase during the first 40 min; in the two 100-min insulin experiments, it did rise during the final 50 min, however. To determine the effect of an A- and B-cell secretogogue on IRS release, we perfused 20 mM arginine for 60 min in six experiments. In all, IRS rose within 3 min and reached a level 71-465% above the control, remaining significantly elevated throughout the perfusion, while glucagon and insulin rose to peak levels at 2 min and then declined somewhat despite continuing arginine perfusion. The results indicate that perfusion of the normal dog pancreas with high doses of glucagon or arginine is accompanied by a prompt increase in IRS release and are compatible with a local feedback circuit involving A- and D-cells. Insulin appears not to augment IRS release, at least not promptly, but IRS stimulated by local endogenous glucagon could inhibit the B-cell response to locally secreted glucagon and thereby influence the composition of the insulin/glucagon secretion mixture.
Biogenesis of poxviruses: analysis of the morphogenetic sequence using a conditional lethal mutant defective in envelope self-assembly.
Authors: Stern W , Pogo B G , Dales S
Published: May 2006

A conditional lethal, temperature-sensitive mutant of vaccinia, defective in assembly of the virus envelope and maturation, was characterized and shown to mimic exactly the aberrations produced by rifampicin. Analyses of the infection at restrictive and permissive temperatures were conducted with electron microscopy, isotopic pulse-chase experiments in which polypeptides were separated by polyacrylamide slab gels, and assays of core enzymatic activities. The data collected by several approaches reveal that assembly and maturation of vaccinia involves a tightly coupled sequence of interrelated events including the assembly of the envelope, post-translational cleavage of several virion polypeptides, and induction of the core enzymes.
Nerve growth factor in mouse serum and saliva: role of the submandibular gland.
Authors: Murphy R A , Saide J D , Blanchard M H , Young M
Published: May 2006

The concept that the salivary gland of the mouse is an endocrine organ for nerve growth factor (NGF) has been reexamined. Serum concentrations of the protein have been measured by radioimmunoassay in male and female mice and in mice from which the submandibular glands were removed. In spite of the fact that the submandibular glands of male mice contained more NGF than did those of female mice, no sex differences in circulating concentrations of the factor were detected. Furthermore, serum concentrations of NGF did not change after submandibular gland removal or after administration of several autonomic agonists. These results indicate that the submandibular glands are not endocrine organs with respect to NGF. On the other hand, extremely high concentrations of the factor are normally secreted in mouse saliva at levels that reflect the sex differences in the amount of NGF present in the glands. This finding suggests that the salivary gland is an exocrine organ for NGF and that the protein may play a biological role in saliva.
Formation of the four isomers of hen egg white lysozyme containing three native disulfide bonds and one open disulfide bond
Authors: Acharya A. Seetharama , Taniuchi Hiroshi
Published: May 2006

Reduced partially carboxymethylated hen egg white lysozyme (mucopeptide
N
-acetylmuramoylhydrolase; EC 3.2.1.17) (approximately 0.8 mol of [
1
-
14
C]carboxymethyl groups) was air oxidized at pH 8.0 and 37° in the presence of 1.5 mM 2-mercaptoethanol for 36 hr. Gel filtration of this product gave the lower (native) and higher hydrodynamic volume forms, both containing radioactivity (approximately 35 and 65%, respectively). Ion exchange chromatography of the lower hydrodynamic volume forms yielded renatured lysozyme, two major radioactive samples (LH
C
and LH
D
) eluting at the positions of monocarboxymethylated lysozyme, and two minor radioactive samples eluting at the positions of dicarboxymethylated lysozyme. Sample LH
C
(approximately 23% of the radioactivity) was essentially homogeneous with respect to electrophoretic mobility, exhibited approximately 39% of the enzymic activity of lysozyme, and contained 0.95 mol of [
14
C]carboxymethyl groups. Sample LH
D
(approximately 8% of the radioactivity) was also enzymically active and contained approximately 0.5 mol of [
14
C]carboxymethyl groups; this low value is apparently due to contamination of noncarboxymethylated species. The radioactive tryptic peptides from samples LH
C
and LH
D
were characterized. The results indicated that all eight isomers, containing three presumably native disulfide bonds and one free and one carboxymethylated sulfhydryl group, are formed on air oxidation of reduced partially carboxymethylated lysozyme. Since in each of these isomers the formation of one of the four native disulfide bonds is permanently blocked, it would follow that no one of the four disulfide bonds of native lysozyme is obligatory in the formation of the other three native disulfide bonds.