bluuebunny/crossref_metadata_2025 huggingface dataset:
Random walk analysis of potassium fluxes associated with nerve impulses.
Authors: Clay J R , Shlesinger M F
Published: May 2006

We present a novel recursion method for obtaining theoretical expressions for unidirectional single-file fluxes of ions through narrow membrane channels containing an arbitrary number of ion sites. The theory is applied to experimental tracer fluxes associated with nerve impulses from cephalopod giant axon membranes at various temperatures between 7 degrees and 27 degrees. The comparison between the theoretical and experimental one-way fluxes suggests that the potassium channel in nerve membrane contains three ion sites, which is consistent with the deduction by Hodgkin and Keynes that the potassium channel contains two or three sites on the basis of the ratio of tracer influx to tracer efflux. The analytical results in this paper provide a further test of the single-file model for nerve and other membrane preparations.
Stimulation of sugar uptake and thymidine incorporation in mouse 3T3 cells by calcium phosphate and other extracellular particles.
Authors: Barnes D W , Colowick S P
Published: May 2006

Evidence is presented that the marked stimulation of sugar uptake and thymidine incorporation by addition of extra Ca2+ to stationary phase mouse 3T3 cells in culture is phosphate dependent and due to the action of the calcium phosphate precipitate formed in the medium. The cells are similarly stimulated by a variety of particulate materials, including calcium pyrophosphate, barium sulfate, kaolin, and polystrene beads. The precipitate effects on sugar uptake are of the same magnitude as those seen with certain hormones (insulin, epidermal growth factor) or with fresh 10% calf serum. The effect of barium sulfate on thymidine incorporation is also of the same magnitude as seen with these hormones, but much less than half that found with fresh calf serum. The stimulation by barium sulfate or hormones of thymidine incorporation is not phosphate dependent.
Evidence for ovarian “inhibin”: Suppression of the secondary rise in serum follicle stimulating hormone levels in proestrous rats by injection of porcine follicular fluid
Authors: Schwartz Neena B. , Channing Cornelia P.
Published: May 2006

The present studies were carried out to see if porcine follicular fluid could inhibit increases in serum follicle stimulating hormone (FSH) levels when injected into the rat. For these studies the pentobarbital-treated proestrous rat was chosen as the major test animal model. If an artificial surge of luteinizing hormone (LH) is administered to these rats, it can induce a synchronized secondary rise in FSH secretion rate. Normal saline-treated rats were also used as test animals. They exhibit preovulatory endogenous “surges” of LH and FSH, and also a secondary FSH rise.

Porcine follicular fluid was harvested from medium-sized and large (3- to 10-mm diameter) follicles and treated with charcoal to remove endogenous steroids. Charcoal-treated porcine serum served as a control solution. The fluid was injected intraperitoneally in two 0.5-ml doses into pentobarbital-treated proestrous rats immediately and 3 hr after LH injection. Follicular fluid, but not the serum, suppressed the secondary, LH-induced FSH rise (
P
< 0.01) in a dose-dependent manner, without altering the effects of LH upon serum ovarian steroid levels or follicular rupture. It was effective down to a total dose of 200 μl. Porcine follicular fluid also blocked the secondary FSH surge in normal proestrous rats exhibiting endogenous LH/FSH primary surges. Thus, it would appear that porcine follicular fluid contains a non-steroidal substance(s) that can block the secretion of FSH that is secondary to a natural or artificial LH surge.
Enkephalin: conformational analysis by means of empirical energy calculations.
Authors: Isogai Y , Némethy G , Scheraga H A
Published: May 2006

Low-energy conformations of methionine-enkephalin were generated by means of an empirical method of computation. Many compact conformations, including those containing various standard bends, were of comparable energy. However, one conformation was found to have a potential energy about 5 kcal/mol (21 X 10(3) J/mol) below that of the large group of compact conformations. In this conformation, the 3-glycyl and 4-phenylalanyl residues form a bend of type II'. The conformation is stabilized by a hydrogen bond between the OH group of the 1-tyrosine side chain and the C==O group of 3-glycine or 4-phenylalanine. The phenylalanine and methionine side chains are relatively unrestricted. The conformation is consistent with published nuclear magnetic resonance parameters--coupling constants, temperature dependence of the chemical shift, and spin-lattice relaxation times. It is likely that the molecule undergoes a conformational change when it is bound to the receptor. Leucine-enkephalin appears to have the same conformation as its methionine homolog.
Nerve growth factor receptors on human melanoma cells in culture.
Authors: Fabricant R N , De Larco J E , Todaro G J
Published: May 2006

Purified mouse nerve growth factor (NGF)radiolabeled with 125I was tested for its ability to bind to a variety of different cultured cells. NGF binds readily to human and hamster melanoma cells but does not bind to many other cell lines. The three cell lines with the highest number of NGF receptors were derived from metastatic melanomas. One of these lines, A875, was studied in detail and was shown to have approximately 7x10(5) NGF receptors per cell with an association constant of 1.0x10(9) liters/mole. The use of these cells in competition binding assays permits the detection of 0.25 ng of NGF in various biologic fluids. NGF can be shown to increase the survival, but not the division, of melanoma cells maintained in medium depleted of serum growth factors. This effect of NGF as a specific "survival factor" appears analogous to its effect on cultured sympathetic ganglion cells and on other cells derived from the neural crest.
Gonadotropin-induced regulation of luteinizing hormone receptors and desensitization of testicular 3':5'-cyclic AMP and testosterone responses.
Authors: Hsueh A J , Dufau M L , Catt K J
Published: May 2006

Administration of human chorionic gonadotropin (hCG) to male rats was followed by dose-related changes in luteinizing hormone (LH) receptors in the testis. After treatment with a low dose of hCG (10international units), the number of LH receptors increased slightly over the first 24 hr, then fell to about 30% of the control value. These changes occurred with occupancy of only 8% of the available receptors, and were initially accompanied by increased basal testosterone production in vitro with no change in basal 3'5'-cyclic AMP production. During stimulation with hCG in vitro, such testes showed a transient decrease in cyclic AMP response on the first day after gonadotropin treatment and no change in testosterone response. By contrast, a 20-fold higher dose of hCG caused more rapid and complete loss of LH receptors, with major and transient occupancy of receptors at 24 hr and marked elevations of basal cyclic AMP and testosterone production in vitro. The initial occupancy of receptors was accompanied by a rapid fall in the cyclic AMP response to hCG in vitro, and was followed by marked receptor loss and inhibition of the cyclic AMP response for up to 5 days. The testosterone response to hCG in vitro was completely inhibited for about 3 days, then rose to the control level at 5 days, when only a small proportion of the original receptor sites and cyclic AMP response had begun to return. Such complete recovery of the steroidogenic response when only a fraction of the receptor population had returned was consistent with the presence of receptor reserve or "spare" receptors in the testis. These studies have demonstrated that negative regulation of LH receptors by exogenous gonadotropin is accompanied by consequent changes in cyclic AMP and testosterone responses to hCG in vitro. Hormone induced desensitization of interstitial cell responses was initially related to occupancy of LH receptors and later to a protracted loss of receptor sites.
Appearance of a chromatin protein during the erythroid differentiation of Friend virus-transformed cells.
Authors: Keppel F , Allet B , Eisen H
Published: May 2006

Chromatin proteins from erythroleukemia cells transformed by Friend virus were analyzed by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. A new chromosomal protein, apparent molecular weight 25,000, was shown to appear during erythroid differentiation of the cells induced by dimethyl sulfoxide or hexamethylenebisacetamide. This protein is tightly bound to the chromatin and does not appear to be related to any of the known histones. It is also demonstrated that this protein is not induced in a dimethyl sulfoxide-resistant variant of these cells.
Characterization of C-reactive protein and the complement subcomponent C1t as homologous proteins displaying cyclic pentameric symmetry (pentraxins).
Authors: Osmand A P , Friedenson B , Gewurz H , Painter R H , Hofmann T , Shelton E
Published: May 2006

Partial amino acid sequences of rabbit C-reactive protein, a peptide derived from human C-reactive protein by cyanogen bromide cleavage, and the C1t subcomponent of the human complement component C1 have been determined. Extensive sequence homology between these proteins establish their evolutionary relationships. In addition, examination of C-reactive proteins by negative-stain electron microscopy revealed that the protein is composed of five subunits arranged in cyclic symmetry. This structure is similar to that reported for both C1t and the amyloid P-component. The extensive structural relationship suggests similar or overlapping functions and the term pentraxin is proposed to describe these homologous proteins.
Trans-synaptic induction of adrenomedullary tyrosine hydroxylase activity by choline: evidence that choline administration can increase cholinergic transmission.
Authors: Ulus I H , Hirsch M J , Wurtman R J
Published: May 2006

Twenty-four hours after rats receive choline chloride (20 mmol/kg, by stomach tube) the activity of tyrosine hydroxylase [tyrosine 3-monooxygenase; L-tyrosine, tetrahydropteridine:oxygen oxidoreductase (3-hydroxylating), EC 1.14.16.2] increases by 31% within adrenomedullary chromaffin cells. This treatment also causes major elevations in the levels of choline and acetylcholine within the adrenal gland; however, acetylcholine levels return to normal by 16 hr after the choline is given. The daily administration of 10 or 20 mmol/kg of choline for 4 days elevates adrenal tyrosine hydroxylase activity by 29% or 51%, respectively. Such increases in tyrosine hydroxylase activity are not observed in animals given ammonium chloride, another basic chloride-containing compound, by stomach tube or in animals treated with cycloheximide, an inhibitor of adrenal protein synthesis. They are also absent in denervated adrenals. These observations demonstrate that the increase in presynaptic acetylcholine levels produced by giving animals the neurotransmitter's precursor (choline) can be associated with parallel changes in the transmission of signals across cholinergic synapses, probably because more of the transmitter is released per nerve impulse.
Interaction between mutations of ribosomes and RNA polymerase: a pair of strA and rif mutants individually temperature-insensitive but temperature-sensitive in combination.
Authors: Chakrabarti S L , Gorini L
Published: May 2006

A temperature-sensitive lethal mutant of Escherichia coli has been constructed by combining two temperature-insensitive mutations: a rif180 mutation that modifies RNA polymerase (RNA nucleotidyltransferase; nucleosidetriphosphate:RNA nucleotidyltransferase, EC 2.7.7.6) and a strA24 mutation that modifies the ribosomal protein S12. The temperature sensitivity is a property of the combination of these two particular alleles; replacement of either of the alleles relieves the temperature sensitivity. An isogenic strain containing a different strA mutation (i.e., rif180 strA11) is not temperature sensitive. Evidently ribosomes modified by the particular strA24 polymerase altered by the rif180 mutation, which suggests that in vivo there may exist some interaction between structures of ribosomes and the RNA polymerase.
Effects of naloxone on experimentally induced ischemic pain and on mood in human subjects.
Authors: Grevert P , Goldstein A
Published: May 2006

The hypothesis that painful stimuli activate the endogenous opioid (endorphin) system in humans was tested by examining the effect of the opiate antagonist naloxone on experimentally induced ischemic pain and on subjective mood ratings. Intravenous injections of saline or naloxone hydrochloride (2 and 10 mg) were administered under double-blind conditions to 12 subjects. Naloxone did not affect the pain ratings. However, a significant dose-related effect of naloxone on tension-anxiety was found, suggesting that the endorphins. like exogenously administered opiates, may have antianxiety properties.
Mechanism of tertiary structural change in hemoglobin.
Authors: Gelin B R , Karplus M
Published: May 2006

A reaction path is presented by which the effects of oxygen binding in hemoglobin are transmitted from a heme group to the surface of its subunit. Starting from the known deoxy geometry, it is shown by calculations with empirical energy functions and comparisons with available data how the change in heme geometry on ligation introduces a perturbation that leads to the tertiary structural alterations essential for cooperatively. It is found that there is little strain on the unliganded heme; instead, the reduced oxygen affinity of hemoglobin results from the strain on the liganded subunit in a tetramer with the deoxy quarternary structure.
Induction of functional beta-adrenergic receptors in HeLa cells.
Authors: Tallman J F , Smith C C , Henneberry R C
Published: May 2006

HeLa cells contain beta-adrenergic receptors that are characterized by specific binding of I[3H]dihydroalprenolol, increased 3':5'-cyclic AMP production in intact cells after incubation with l-isoproterenol, and increased adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] activity in the presence of l-isoproterenol. After cells were cultured with butyrate, the number of beta-adrenergic receptors, cyclic AMP production in intact cells, and adenylate cyclase activation by l-isoproterenol were increased severalfold over those of untreated cells. The increase involved the induction of synthesis of new receptor molecules with identical affinities for l-[3H]-dihydroalprenolol; all three processes were blocked by cycloheximide and actinomycin D. This induction was relatively specific for butyric acid and only the closely related short-chain fatty acids, propionic and valeric acids, were capable of partially inducing the same effect. In contrast to induction of beta-adrenergic binding sites, there was no increase in basal or fluoride-activated adenylate cyclase activity, indicating that the beta-adrenergic receptor and adenylate cyclase and different molecules that may be controlled separately.
Cell wall extension in Nitella as influenced by acids and ions.
Authors: Métraux J P , Taiz L
Published: May 2006

The giant internode cells of Nitella axillaris exhibit acid-induced growth similar to that found in higher plants. The threshold pH is 4.5, with a maximum at 3.5. The acid growth effect is transient, lasting no more than 32 min. Extensibility measurements of isolated cell walls showed a similar pattern of acid enhancement. Prolonged boiling in water (12 hr) only partially inhibited the acid-induced wall extensibility and actually increased the extensibility at pH 6. It was concluded that physical, rather than enzymatic, processes were responsible for acid-enhanced continuous extension ("creep") in Nitella walls. A complex cation-sensitive mechanism that affects extensibility was also characterized. Among the stimulatory (wall-softening) cations, divalents were generally more effective than monovalents, with magnesium being the most stimulatory. The inhibitory (wall-hardening) cations included divalents and trivalents, aluminum being the most inhibitory. Ionic effects on extensibility were even less sensitive to prolonged boiling in water than acid effects.
Energy-structure correlation in metalloporphyrins and the control of oxygen binding by hemoglobin.
Authors: Warshel A
Published: May 2006

The contribution of the porphyrin skeleton to the potential energy surface metalloporphyrins is calculated by the semiempirical method of quantum mechanical extension of the consistent force field to eta electron molecules. This calculation makes it possible to correlate the observed structure of metalloporphyrins with the strain energy of the porphyrin skeleton. It is found that the out-of-plane metal displacement in pentacoordinate heme systems is due to both the restricted size of the porphyrin hole and the "1-3" steric interaction between the axial ligand and the heme nitrogens. The main components of the active site of hemoglobin are simulated by a histidine-heme-oxygen system. The energy surface of this system provides a quantitative explanation for the control of ligand binding by hemoglobin. It is shown that the heme acts as a diaphragm, designed to provide simultaneous binding to the histidine and the sixth ligand under the steric requirements of the 1-3 interactions. The dependence of the hemoglobin potential surface on the distance between the proximal histidine and the heme plane is evaluated for the R and T states, using the calculated heme potential and the observed energy of heme-heme interaction.
Extended Watson integrals for the cubic lattices
Authors: Glasser M. L. , Zucker I. J.
Published: May 2006

The known exact expressions for extended Watson integrals relating to various cubic and modified cubic lattices are summarized. A new closed form expression for Watson's result on the simple cubic lattice is given in terms of gamma functions.
Chromosomal location of a structural gene for the RNA polymerase sigma factor in Escherichia coli.
Authors: Nakamura Y , Osawa T , Yura T
Published: May 2006

A set of F' strains of Escherichia coli K-12 partially diploid for various chromosomal segments has been examined for possible gene dosage effects in the synthesis of sigma factor of the DNA-dependent RNA polymerase (RNA nucleotidyltransferase; nucleoside-triphosphate:RNA nucleoti-dyltransferase, EC 2.7.7.6). It was found that all F' strains diploid for the dnaG region synthesize sigma at rates two to three times higher than other F' or F- strains. Moreover, strains of Salmonella typhimurium harboring these F' plasmids produce E. coli sigma in addition to Salmonella sigma. This has been shown on the basis of the finding that Salmonella sigma can be precipitated with antiserum against E. coli RNA polymerase but is distinguishable from E. coli sigma in its mobility in sodium dodecyl sulfate/polyacrylamide gel electrophoresis. E. coli sigma polypeptides thus produced seem to be stable in cells of S. typhimurium. These results indicate that a structural gene for sigma (rpoD) is located at the metC-argG region, probably near the dnaG locus (66 min on the current genetic map of E. coli).
Primary structure of very low density apolipoprotein C-II of human plasma.
Authors: Jackson R L , Baker H N , Gilliam E B , Gotto A M
Published: May 2006

Apolipoprotein C-II (apoC-II), a protein constituent of very low density lipoproteins of human plasma and the activator protein of lipoprotein lipase, has been isolated and its amino acid sequence has been studied. The protein has 78 amino acid residues and is lacking cysteine, cystine, and histidine. Chromatography on Bio-Gel P-30 in 25% formic acid of the cyanogen bromide digest of apoC-II yields three fragments designated as CNBr-I, -II, and -III. They contained 50, 19, and 9 residues, respectively. The alignment of the cyanogen bromide fragments has been established as CNBr-III-I-II by isolation and sequence of the tryptic peptides of the intact protein. The amino acid sequences of the tryptic and CNBr peptides were determined by conventional methods. With this information, it was possible to establish the complete amino acid sequence of apoC-II.
Dual role of interfacial phospholipid in phospholipase A2 catalysis.
Authors: Roberts M F , Deems R A , Dennis E A
Published: May 2006

The results of crosslinking experiments with dimethyl suberimidate and gel filtration binding studies are used to delineate a detailed model for phospholipase A2(phosphatide 2-acyl-hydrolase, EC 3.1.1.4) action in the presence of Ca2+ on mixed micelles of Triton X-100 and phospholipid. Important features of the "dual-phospholipid" model are: (i) the use of the nonionic surfactant as an inert matrix that may influence lipid conformation but does not interact with the enzyme; (ii) the involvement of two lipid molecules in a single cycle of catalysis as an explanation for the "surface dilution" phenomenon; (iii) the requirement of an ordered reaction whereby divalent metal ion binds prior to phospholipid binding; and (iv) the induction by lipid substrate of an asymmetric dimer structure for the enzyme.
In vivo analysis of cellular replication.
Authors: Schneider E L , Sternberg H , Tice R R
Published: May 2006

The number of previous cell replications that a metaphase cell has undergone in the presence of BrdUrd can be determined by the differential fluorescent patterns of metaphse chromosomes stained with Hoechst dye 33258. To examine if this technique could be applied to analyzing cell cycle kinetics in vivo, we infused Wistar rats with BrdUrd for 7.5-33 hr at concentrations of the nucleotide analog that did not inhibit cellular replication. Examination of the frequency of one, two, and three or more replication cycle cells as a function of BrdUrd infusion time indicates that cell replication times for rat bone marrow cells are relatively homogeneous. Analysis of this data with a computer simulation model produced a mean cell cycle duration of 9.2 hr, which is compatible with the fastest times obtained with radioisotope studies. These results support the potential of nonradioisotope analysis of cell replication in vivo.
Cell-free synthesis of fish preproinsulin, and processing by heterologous mammalian microsomal membranes.
Authors: Shields D , Blobel G
Published: May 2006

Poly(A)-containing mRNA isolated from the islets of Langerhans obtained from two species of fish, angler fish (Lophius americanus) and sea raven (Hemitripterus americanus), stimulated protein synthesis 16-fold in a wheat germ cell-free system. Characterization of the translation products by polyacrylamide gel electrophoresis in sodium dodecyl sulfate showed a major polypeptide weighing 11,500 daltons that was specifically precipitated by an antibody against angler fish insulin. Partial sequence analysis of the amino terminal revealed that this polypeptide is preproinsulin, in which the amino terminus of proinsulin is preceded by either 23 (angler fish) or 25 (sea raven) amino acid residues. Translation of fish islet mRNA in a wheat germ cell-free system in the presence of dog pancreas microsomal membranes led to the correct cleavage of the nascent preproinsulin, resulting in the synthesis of authentic fish proinsulin, as verified by partial sequence analysis. Moreover, the synthesized fish proinsulin was segregated, presumably into the luminal space of the dog pancreas microsomal vesicles, because it was found to be resistant to proteolysis by added trypsin and chymotrypsin. Our data thus suggest that the mechanisms and information for the transfer of secretory proteins across the microsomal membrane are highly conserved during evolution.
Enhancement of nonspecific immunity to Klebsiella pneumoniae infection by a synthetic immunoadjuvant (N-acetylmuramyl-L-alanyl-D-isoglutamine) and several analogs.
Authors: Chedid L , Parant M , Parant F , Lefrancher P , Choay J , Lederer E
Published: May 2006

N-Acetylmuramyl-L-alanyl-D-isoglutamine and four other synthetic adjuvants that are structural analogs of part of the mycobacterial peptidoglycan monomer are shown to enhance the nonspecific immunity of mice infected by Klebsiella pneumoniae. These compounds are active by various routes, including oral administration; they are also effective when administered after challenge. Of the seventeen other analogs tested, none is able to increase significantly resistance to infection, although seven of these molecules are adjuvant-active in saline. Previous results have shown that in contrast to lipopolysaccharides, these synthetic adjuvants are devoid of immunogenicity, mitogenicity, and toxicity in normal or adrenalectomized mice.
Inhibition of DNA synthesis in cultures of 3T3 cells by isolated surface membranes.
Authors: Whittenberger B , Glaser L
Published: May 2006

When added to a sparse culture of 3T3 cells, a surface membrane-enriched fraction from 3T3 cells inhibited the rate of DNA synthesis in a time- and concentration-dependent manner. The membrane preparation had no effect on the rate of DNA synthesis of simian virus 40-transformed 3T3 cells. A similar membrane preparation from transformed cells had a lesser inhibitory effect on 3T3 cells and no effect on transformed cells. The inhibition by membranes was reversible. The data suggest that, when added to growing 3T3 cells, 3T3 surface membranes can mimic the effect of increasing cell density on DNA synthesis.
Isolation of amino acid activating subunit-pantetheine protein complexes: Their role in chain elongation in tyrocidine synthesis
Authors: Lee Sung G. , Lipmann Fritz
Published: May 2006

Dissociation of the multienzymes of tyrocidine synthesis by prolonged incubation of crude extracts of
Bacillus brevis
(Dubos strain, ATCC 8185) has yielded, on Sephadex G-100 chromatography, two fractions of amino acid activating subunits, a larger one of 70,000 daltons and a smaller one of 90,000 daltons; the latter was a complex consisting of the 70,000 dalton subunit and the pantetheine-carrying protein of about 20,000 daltons. When it dissociated, the intermediate enzyme, which activates three amino acids, contained two-thirds of the subunits in the 70,000 dalton and one-third in the 90,000 dalton fraction; the heavy enzyme, which activates six amino acids, contained five-sixths of the subunits in the former fraction and one-sixth in the latter. Both fractions showed ATP-PP
i
exchange with all amino acids that are activated by the respective polyenzymes. With proline as an example, the 70,000 dalton subunit exhibited a single low-affinity binding site, which should correspond to the peripheral thiol acceptor site, whereas the 90,000 dalton subunit showed both a low-affinity binding site and an additional high-affinity site for proline; the high-affinity site is attributed to the pantetheine present on the pantetheine-carrying protein, and suggests that amino acids are translocated from the peripheral SH to the pantetheine-carrying moiety during chain elongation. This was confirmed by the observation that the 90,000 dalton complex, when incubated with the light enzyme in the presence of phenylalanine and proline, produced DPhe-Pro dipeptide that cyclized into DPhe-Pro diketopiperazine, but the 70,000 dalton activating subunit, when similarly incubated, did not. After subunit dissociation, however, no further elongation occurred after the transfer from phenylalanine to proline.
Effects of thyrotropin on the thyroid cell membrane: Hyperpolarization induced by hormone-receptor interaction
Authors: Grollman Evelyn F. , Lee George , Ambesi-Impiombato F. S. , Meldolesi Maria F. , Aloj Salvatore M. , Coon Hayden G. , Kaback H. Ronald , Kohn Leonard D.
Published: May 2006

Cultured thyroid cells accumulate the lipophilic cation triphenylmethylphosphonium, indicating that there is an electrical potential (interior negative) across the plasma membrane. Thyrotropin stimulates the uptake of the lipophilic cation 3-fold, and the proton conductor carbonylcyanide-
m
-chlorophenylhydrazone causes efflux of triphenylmethylphosphonium accumulated in the presence or absence of thyrotropin. The stimulatory effect of thyrotropin on triphenylmethylphosphonium accumulation is not mimicked by human chorionic gonadotropin, a glycoprotein hormone with a similar structure whose target organ is not the thyroid, and the effect is abolished if the thyrotropin-receptor activity of the cells is destroyed by treatment with trypsin. Analogous effects are observed with thyroid plasma membrane vesicles which are essentially devoid of mitochondrial and soluble enzyme activities. Triphenylmethylphosphonium uptake and stimulation by thyrotropin occurs when NaCl, KCl, or Tris·HCl concentration gradients are artifically imposed across the vesicle membrane ([salt]
out
> [salt]
in
). It seems likely, therefore, that triphenylmethylphosphonium uptake is driven by a chloride diffusion potential (interior negative) and that thyrotropin either increases the permeability of the membrane to anions or decreases its permeability to cations. Thyrotropin-stimulated triphenylmethylphosphonium uptake in the vesicle preparations reaches a quasi steady-state within 3 min; in contrast, thyrotropin-stimulated adenylate cyclase activity is negligible during this period of time, becomes measurable after about 4 min, and is optimal after 12-15 min. Thus, a primary mode of action of thyrotropin on the thyroid cell may be an alteration in the electrical potential across the plasma membrane. The relevance of this observation to the mechanism of action of other glycoprotein hormones, certain bacterial toxins, and interferon is discussed.
A role for asparaginyl-tRNA in the regulation of asparagine synthetase in a mammalian cell line.
Authors: Arfin S M , Simpson D R , Chiang C S , Andrulis I L , Hatfield G W
Published: May 2006

The expression of asparagine synthetase activity [L-aspartate:ammonia ligase (AMP-forming), EC 6.3.1.1] in cultured Chinese hamster ovary (CHO) cells is regulated by asparagine. After transfer of CHO cells from an asparagine-supplemented medium to a medium lacking asparagine, activity increases 1.5- to 2-fold. If asparagine is added back to the medium, activity returns to control levels. To test the possible involvement of Asn-tRNAAsn in regulating the levels of asparagine synthetase, we have examined the levels of asparagine synthetase in a mutant of CHO cells containing a temperature-sensitive asparaginyl-tRNA synthetase [L-asparagine:tRNA ligase (AMP-forming), EC 6.1.1.22]. Under conditions of limited asparaginyl-tRNA synthetase activity in the mutant, there is a 2- to 3-fold increase in the level of asparagine synthetase activity. Under identical conditions, there is no change in asparagine synthetase activity in the wild type. This correlation between asparaginyl-tRNA synthetase activity and asparagine synthetase levels may be a consequence of a direct role of tRNAAsn in the regulation of the in vivo expression of the asparagine synthetase structural gene.
Crosslinked histone octamer as a model of the nucleosome core.
Authors: Stein A , Bina-Stein M , Simpson R T
Published: May 2006

When histones in chromatin core particles were crosslinked with dimethylsuberimidate, the resulting particles had properties closely similar to those of native core particles. A crosslinked octameric histone complex was isolated from these particles under nondenaturing conditions. Upon reaction with DNA, this octameric protein folded the DNA into a structure closely resembling that of native core particles as verified by various techniques; protein denaturants were necessary for reassociation. The histone octamer is useful as a model of the nucleosome protein core and for studying histone-DNA interactions that occur in nucleosomes.
Sugar uptake into brush border vesicles from normal human kidney.
Authors: Turner R J , Silverman M
Published: May 2006

Uptake studies of simple sugars were performed on a membrane fractions containing osmotically active vesicles prepared from normal human kidney cortex. The uptake of D-glucose was found to be sodium-dependent and phlorizin-sensitive. The specificity of the D-glucose transport mechanism is such that it is shared by alpha-methyl-D-glucoside, D-galactose, and 5-thio-D-glucose, while 2-deoxy-D-glucose, 3-O-methyl-D-glucose, D-mannose, and D-fructose show little, if any, affinity. Measurement of the sodium-dependent component of the initial D-glucose uptake as a function of glucose concentration resulted in a curvilinear Scatchard plot, indicating the possibility of cooperative effects, or alternatively, the existence of two (or more) sodium-dependent D-glucose transporters. In the case of two transporters, we estimate that Km congruent to 0.3 mM and Vmax congruent to 2.5 nmol/min per mg of protein for the "high-affinity transporter," and Km approximately 6 mM and Vmax approximately 8 nmol/min per mg of protein for the "low-affinity transporter." These specificity and kinetic properties strongly suggest that the sodium-dependent D-glucose transport mechanism characterized in our studies is localized to the brush border of the proximal tubule.
Synthesis of full-length DNA copies of avian myeloblastosis virus RNA in high yields.
Authors: Myers J C , Spiegelman S , Kacian D L
Published: May 2006

The synthesis of full-length complementary DNA copies of avian myeloblastosis virus RNA is described. The cDNA is estimated by electrophoresis in agarose-methylmercury gels to have a molecular weight of 2.6 X 10(6), equivalent in size to that of the RNA template. Most (60-70%) of the reaction product is the full-length material and yields correspond to 60-70% of the input RNA.
Effects of antitubulins on the redistribution of crosslinked receptors on the surface of fibroblasts and epithelial cells
Authors: Domnina L. V. , Pletyushkina O. Y. , Vasiliev J. M. , Gelfand I. M.
Published: May 2006

Substrate-attached normal mouse fibroblasts, transformed mouse fibroblasts (L strain), and epithelial cells (MPTR strain) were incubated with two ligands crosslinking different groups of the surface receptors: concanavalin A and cationic ferritin. Surface-attached ligands were revealed by an indirect immunofluorescence method. Incubation of control cells with these ligands induced the patching of corresponding surface receptors and the clearing of these receptors from the surface zones located on the lamellar cytoplasm near cell edges actively protruding pseudopodia.

Effects of three antitubulins (microtubule-destroying drugs: Colcemid, colchicine, and vinblastine) on the ligand-induced redistribution of receptors were investigated and compared with the previously described effects of these drugs on the distribution of active cell edges. Incubation of normal and transformed fibroblasts with these antitubulins led to the disappearance of nonactive cell edges; the whole cell perimeter became active. Correspondingly, the clearing pattern of the surface receptors of fibroblasts was altered by antitubulins: the cleared area in antitubulin-treated cells formed a circular band along the whole peripheral cell edge. In epithelial cultures, in contrast to fibroblastic ones, antitubulins changed neither the distribution of the active sites of the surface nor the distribution of the areas cleared of crosslinked receptors. Thus, the specific ability of the surface areas located near the active cell edges to become cleared of crosslinked receptors is characteristic not only for the cells with intact microtubules, but also for the cells with microtubules destroyed with antitubulins.
Detection of active heteropolymeric beta-glucuronidase in hybrids between mouse cells and human fibroblasts with beta-glucuronidase deficiency.
Authors: Chern C J
Published: May 2006

Heteropolymeric beta-glucuronidases are detected in somatic cell hybrids between mouse cells and human fibroblasts deficient in beta-glucuronidase (beta-D-glucuronide glucuronosohydrolase, EC 3.2.1.31) by electrophoresis and column chromatography. Specific antisera against human beta-glucuronidase prepared in mice recognize these heteropolymeric beta-glucuronidases. Our results demonstrate that synthesis of mutant subunits of variant beta-glucuronidase continues in deficient human fibroblasts; these mutant subunits of human beta-glucuronidase retain the ability to associate with normal subunits of mouse beta-glucuronidase to form the enzymatically and immunologically active tetramer. These studies demonstrate the usefulness of interspecific cell hybrids for study of structural gene mutations of polymeric enzymes, such as those of beta-glucuronidase in mucopolysaccharidosis type VII.
Mechanisms by which diazepam, muscimol, and other drugs change the content of cGMP in cerebellar cortex
Authors: Biggio G. , Brodie B. B. , Costa E. , Guidotti A.
Published: May 2006

The cerebellum consists of two parts: the cerebellar nuclei whose connections to the various parts of the central nervous system coordinate muscle movements, and the cerebellar cortex which exerts an inhibitory influence on the cerebellar nuclei through the release of γ-aminobutyric acid (γAbu) from Purkinje cells. The activity of Purkinje cells is regulated by two excitatory inputs to the cerebellar cortex—the climbing and mossy fibers—and by a neuronal network within the cortex which inhibits the activity of Purkinje cells through the release of γAbu from interneurons. The net activity of Purkinje cells is related to their content of guanosine 3′:5′-cyclic monophosphate (cGMP) which increases or decreases according to changes in the activity of climbing and mossy fibers as well as to changes in the activation of γAbu receptors. When these receptors are activated, the cGMP of Purkinje cells decreases; when they are inhibited, the cGMP increases.

The cGMP content of the cerebellar cortex is altered by drugs that change either the excitatory input of climbing or mossy fibers or the inhibitory input mediated by the activation of γAbu receptors. Mechanisms by which various drugs alter the cerebellar content of cGMP were investigated. By using various experimental designs, it was shown that diazepam and muscimol lowered the cGMP content by activating γAbu receptors. In contrast, morphine and haloperidol lowered the cerebellar cortex cGMP by decreasing the excitation of mossy fibers whereas harmaline increased the cGMP by increasing the excitation of the climbing fibers.
Molecular events and energy changes during the action potential.
Authors: Margineanu D G , Schoffeniels E
Published: May 2006

A novel interpretation of the existing data concerning the energy changes associated with nerve impulse propagation is proposed. The main conclusion is that the negative phrase ofthe initial heat of activity cannot be accounted for without recourse to conformational changes in membrane proteins. It stems from analyzing and computing the energy changes associated with ionic flows, capacitive currents, and structural changes in membrane gateways. A close quantitative agreement with microcalorimetric measurements was achieved.
Separation and infectivity of circular and linear forms of potato spindle tuber viroid.
Authors: Owens R A , Erbe E , Hadidi A , Steere R L , Diener T O
Published: May 2006

Potato spindle tuber viroid can be separated into two fractions by polyacrylamide gelelectrophoresis in the presence of formamide and urea. One fraction contains predominantly circular molecules; the second fraction contains almost exclusively linear molecules. The purity of the fractions was estimated by electron microscopy of formaldehyde-denatured molecules. The length distributions of denatured circular and linear molecules were determined. Both circular and linear molecules were found to be infectious.
Low-molecular-weight peptide inhibits RNA synthesis in human leukemic and phytohemagglutinin-stimulated leukocytes and globin mRNA transcription in differentiating Friend cells.
Authors: Amici D , Rossi G B , Cioé L , Matarese G P , Dolei A , Guglielmi L , Gianfranceschi G L
Published: May 2006

The RNA synthesis of human leukemic leukocytes and phytohemagglutinin-stimulated lymphocytes is markedly reduced by administration of a low-molecular-weight nonhistone peptide factor from calf thymus. Treatment with the factor strongly inhibits hemoglobin production and globin mRNA transcription in dimethyl sulfoxide-stimulated Friend cells without appreciably modifying the rate of cell growth. Evidence for specificity of these effects is provided by the lack of action of the factor on both growth rate and RNA synthesis of a number of nondifferentiating cell lines from various animal species. After removal of the compound, both human lymphocytes and Friend cells can be stimulated by phytohemagglutinin and by dimethyl sulfoxide, respectively, ruling out any toxic effect.
Interaction of coagulation factor Xa with human platelets.
Authors: Miletich J P , Jackson C M , Majerus P W
Published: May 2006

When human 125I-labeled Factor Xa is incubated with washed platelets, prothrombin, and Ca2+, a small amount of thrombin is formed which causes the platelet release reaction after a period of time that decreases as the Xa concentration is increased from 0.9 to 19 ng/ml. After a further lag period, the Xa binds reversibly to receptors on the platelet surface and rapid thrombin formation follows (3 units or 1 mug of thrombin formed per min per ng of Xa bound to 10(8) platelets). When platelets are treated with either htrombin (0.5 units/ml) or calcium ionophore A23187 prior to addition of Xa, binding begins immediately. Thrombin formation occurs at the platelet surface at rates that correlate with the amount of Xa bound. Dibutyryl cyclic AMP inhibits the release reaction, Xa binding, and rate of thrombin generation in parallel. The platelet Xa receptor is distinct from the previously described thrombin receptor and appears to be a protein because treatment of platelets with thrombin at 50 units/ml destroys Xa binding sites. The results suggest that specific receptors for Xa appear on the platelet surface after the release reaction occurs. The bound Xa catalyzes thrombin formation 1000-fold faster than does Xa added to reactions in which phospholipids are substituted for platelets.
Action potentials occur in cells of the normal anterior pituitary gland and are stimulated by the hypophysiotropic peptide thyrotropin-releasing hormone.
Authors: Taraskevich P S , Douglas W W
Published: May 2006

Electrical activity in the form of action potentials (spikes) was discovered in normal anterior pituitary cells obtained from rats by tissue dissociation and maintained in culture. Passage of outward current through the microsuction electrodes used for recording often increased spike frequency in spontaneously active cells or initiated spikes in cells previously electrically silent. Spiking persisted in the presence of tetrodotoxin and in the absence of sodium, but was inhibited by the calcium blockers D600 and lanthanum. Such spikes appear, therefore, to be calcium spikes, but contributions to spiking by other ions are not excluded. The stimulant hypophysiotropic peptide thyrotropin-releasing hormone elicited spiking in about ten percent of the cells on which it was tested. These cells are possibly thyrotrophs and mammotrophs, the physiological target cells for this hormone. These results, considered along with existing evidence that adenohypophyseal secretion requires calcium and is elicited by calcium ionophores, prompt the conclusion that action potentials involving calcium influx participate in stimulus-secretion coupling in the anterior pituitary. It may be by stimulating or modulating such electrical activity (with hypophysiotropic hormones) that the brain regulates anterior pituitary secretion.
Membrane-bound neuraminidase from calf brain: regulation of oligosialoganglioside degradation by membrane fluidity and membrane components.
Authors: Sandhoff K , Pallmann B
Published: May 2006

The degradation of lipophilic ganglioside GD1a and hydrophilic sialyllactitol by membrane-bound neuraminidase (EC 3.2.1.18) from calf brain has been studied at substrate concentrations of 0.1 mM. Ganglioside GD1a taken up by cell membranes is hydrolyzed faster membrane-bound neuraminidase than are water-soluble substrates of the enzyme, sialyllactitol and des-GD1a. Availability and enzymic breakdown of the disialoganglioside are enhanced by general anesthetics such as N2O or halothane whereas the degradation of the hydrophilic substrate silayllactitol is not affected or even is decreased by these agents. General anesthetics lower the microviscosity of membranes as indicated by studies of fluorescence depolarization with the indicator 1,6-diphenylhexatriene. Increased fluidity can result in higher lateral diffusion of ganglioside GD1a, thus increasing its chances of presentation to, and interaction with, membrane-bound neuraminidase. Lipophilic derivatives of the disialoganglioside, gangliosides GM1 and GM2 and gangliotriaosylceramide GA2, are strong inhibitors of the ganglioside degradation whereas water-soluble derivatives des-GM1, des-GM2, N-acetylneuraminic acid, and sialyllactose are not. A model is presented that suggests that the activity of membrane-bound neuraminidase on gangliosides of brain membranes is regulated by the viscosity of these membranes and their monosialoganglioside content.
Binding to saxitoxin to electrically excitable neuroblastoma cells.
Authors: Catterall W A , Morrow C S
Published: May 2006

Saxitoxin inhibits the action potential Na+ ionophore of electrically excitable neuroblastoma cells with a KI of 3.7 nM. Binding experiments detect a single class of saturable binding sites with KD = 3.9 nM and a binding capacity of 156 fmol/mg of cell protein (78 sites per micrometer2 of cell surface). Saturable binding is completely inhibited by tetrodotoxin but is unaffected by scorpion toxin or batrachotoxin. No saturable binding is observed in cultures of clone N103, a variant neuroblastoma clone lacking the action potential Na+ response. Thus, saxitoxin binds specifically to the action potential Na+ ionophore in neuroblastoma cells. Comparison of saxitoxin and scorpion toxin binding reveals that there are three saxitoxin receptor sites for each scorpion toxin receptors site. The implications of this stoichiometry are considered.
Inhibition of Rous sarcoma viral RNA translation by a specific oligodeoxyribonucleotide.
Authors: Stephenson M L , Zamecnik P C
Published: May 2006

A tridecamer oligodeoxynucleotide, d(A-A-T-G-G-T-A-A-A-A-T-G-G), which is complementary to reiterated 3'- and 5'-terminal nucleotides of Rous sarcoma virus 35S RNA, is an efficient inhibitor of the translation of proteins specified by the viral RNA in the wheat embryo cell-free system. The inhibition specificity for oncornavirus RNA is greater than for rabbit reticulocyte mRNA or brome mosaic virus RNA. Other oligodeoxynucleotides of similar size have little or no specific effect on the RNA-directed translation. The tridecamer acts as a primer for the avian myeloblastosis virus DNA polymerase when Rous sarcoma virus heated 70S RNA is used as a template, offering evidence that it can hybridize to the RNA. The possible use of such an oligodeoxynucleotide hybridization competitor to inhibit Rous sarcoma virus replication is described in the preceding paper [Zamecnik, P. C. & Stephenson, M. L. (1978) Proc. Natl. Acad. Sci. USA. 75, 280--284].
Macromolecular shape and surface maps by solvent exclusion.
Authors: Greer J , Bush B L
Published: May 2006

A quantitative function equivalent to the "molecular" surface proposed by F. M. Richards [(1977) Annu. Rev. Biophys. Bioeng. 6, 151--176] is defined by the closest approach of solvent spheres to a macromolecule. The function can be used to visualize surface topography, polarity, and charge either as a three-dimensional net or by mapping onto a plane; to calculate surface areas; and to demarcate complementary sites in contacts between subunits. Applications to shape-specific recognition in protein structure and aggregation are discussed.