bluuebunny/crossref_metadata_2025 huggingface dataset:
A transplantable insulinoma in the rat.
Authors: Chick W L , Warren S , Chute R N , Like A A , Lauris V , Kitchen K C
Published: May 2006

A transplantable insulinoma was developed in inbred albino rats of the NEDH strain. The original tumor, 1 cm in diameter, was removed from the pancreas of a male parabiont 566 days folowing 1000 rads (10J/kg) of total body x-irradiation. The time required for implanted fragments to grow to 0.5-1.5 cm in diameter decreased from 5-8 months in the first generation to 2-5 months in the seventh generation. Successful transplantation in male animals followed for 4 or more months after transplantation was significantly greater than in female animals followed for a similar period of time (96% versus 69%). Light and electron microscopy revealed that the tumors consisted predominantly of well-granulated beta cells. Ultrastructural studies also showed small numbers of D-cells. Tumor extracts contained an average of 223 units of immunoreactive insulin and 25.9 mug of immunoreactive somato-statin per gram wet weight of tissue. Tumors generally produced increasingly profound hypoglycemia within 2-4 months following transplantation, with plasma glucose levels frequently falling to 40 mg/100 ml or lower prior to death. Removal of tumors from chronically hypoglycemic animals resulted in transient rebound hyperglycemia with plasma glucose levels above 300mg/100 ml within the first 24 hr and a gradual decline to normal levels of 129 mg/100ml in 2-4 days. These observations correlated with findings of marked atropy and degranulation of the beta cells in the pancreata of tumor-bearing animals, and with gradual return of normal light microscopic morphology following tumor removal.
Roles of proteins from inner face of plasma membranes in susceptibility of of (Na+ + K+)-stimulated Mg2+ adenosinetriphosphatase to ouabain.
Authors: Zachowski A , Lelievre L , Aubry J , Charlemagne D , Paraf A
Published: May 2006

Purified right-side-out (RSO) and inside-out (IO) plasma membrane vesicles release 35% of the total plasma membrane proteins after EDTA treatment. After such a treatment both types of vesicles exhibited the same total activity of (Na+ + K+)-stimulated Mg2+ adenosinetriphosphatase (ATPase; ATP phosphohydrolase, EC 3.6.1.3) as in their native state. The EDTA treatment increases the enzyme sensitivity to ouabain by 350-fold in IO vesicles while being without any effect RSO vesicles. Thus, proteins released only from the IO vesicles led to a change in ouabain sensitivity of the (Na+ + K+)-stimulated Mg2+ ATPase. Moreover, only proteins released from IO vesicles, when added to treated IO vesicles with divalent cations, were able to restore the original resistance of the enzyme to ouabain; released proteins from RSO vesicles failed to make such a reconstitution. Thus, we assume that these proteins detach from the inner face of the plasma membrane upon EDTA treatment and are distinct from the enzyme. Polyacrylamide gel electrophoresis indicates that these inner face plasma membrane proteins are approximately 30,000 daltons.
Presence of corticotropin in brain of normal and hypophysectomized rats.
Authors: Krieger D T , Liotta A , Brownstein M J
Published: May 2006

Immunoreactive and bioreactive corticotropin (ACTH-like) activities have been detected in the median eminence and remaining medial basal hypothalamus of both normal and hypophysectomized adult male rats: bioreactive ACTH (pg/100 mug of protein) 1028 in median eminence and 1289 in medial basal hypothalamus; immunoreactive ACTH (midportion ACTH antibody), 1554 in median eminence and 1887 in medial basal hypothalamus. By use of appropriate antibodies and bioassay, it was demonstrated that immunoreactivity was not due solely to alpha-melanotropin, which has previously been reported to be present in the brain of hypophysectomized animals. The Sephadex G-50 gel filtration patterns determined by immunoassay of column eluates obtained from hypothalamic extracts of normal or hypophysectomized animals were similar but were not identical to the pattern derived from whole pituitary. Immunoreactive (midportion ACTH antibody) ACTH concentrations (pg/100 mug of protein) of other central nervous system areas in normal animals were: cerebellum 34.3, cortex 46.3, thalamus 23.8, and hippocampus 116.3. The total amount of bioreactive ACTH present in the median eminence and medial basal hypothalamus is approximately 1% of that present in the pituitary. The present data suggest that such ACTH may have a diencephalic rather than pituitary origin and raise the question of the functional significance of such ACTH.
Biosynthesis of type I and III collagens by cultured smooth muscle cells from human aorta.
Authors: Layman D L , Epstein E H , Dodson R F , Titus J L
Published: May 2006

The synthesis of collagen by human aortic smooth muscle cells was studied after incubating the cells with [3H]proline and [3H]glycine for 48 hr. The culture medium and cells were lyophilized and then digested with cyanogen bromide (CNBr) in 70% (wt/vol) formic acid. The resultant peptides were subjected to ion exchange chromatography on CM-cellulose and gel filtration on agarose. On the basis of the molar ratios of the alpha1(I)-CB8 and alpha1(III)-CB8 peptides of the alpha1(I) and alpha1(III) chains, approximately one quarter of the collagen synthesized by these cells was identified as type III and three quarters as type I. These data indicate that the smooth muscle can synthesize at least two types of collagen found in the arterial wall.
Effects of ribosomal mutations on the read-through of a chain termination signal: studies on the synthesis of bacteriophage lambda O gene protein in vitro.
Authors: Yates J L , Gette W R , Furth M E , Nomura M
Published: May 2006

In a DNA-dependent protein-synthesizing system that contains streptomycin-sensitive ribosomes, lambda DNA directs the synthesis of two proteins that are products of the O gene. The larger is produced as a result of read-through of a UGA termination codon. In the system containing streptomycin-resistant ribosomes this read-through protein is not synthesized, indicating that the mutational alteration in the ribosomal protein S12 restricts the read-through. The mutant ribosomes also fail to synthesize the read-through coat protein of RNA phage Qbeta. In addition, the mutant ribosomes restrict suppression of amber mutations in vitro, similar to their effect in vivo.
Lymphocytes alloantigens associated with X-chromosome-linked immune response genes.
Authors: Zeicher M , Mozes E , Lonai P
Published: May 2006

A new polymorphic alloantigen system controlled by loci on the X-chromosome has been identified by using antisera from F1 hybrid mice differing in their X-chromosome. These alloantigens are associated with the X-chromosome. These alloantigens are associated with the X-linked immune response genes controlling the immune response to the so-called "thymus independent antigens" such as type III pneumococcal polysaccharide, poly(I)-poly(C), and denatured DNA. They also show association with the histocompatibility locus present on the X-chromosome. They were mainly detected on a not yet characterized thymus-derived lymphocyte subpopulation. A certain similarity with the major histocompatibility complex of the mouse supports the possibility of additional I-like regions besides the I region of the histocompatibility-2 complex.
Demonstration of terminal deoxynucleotidyl transferase in thymocytes by immunofluorescence.
Authors: Goldschneider I , Gregoire K E , Barton R W , Bollum F J
Published: May 2006

The cellular and subcellular distribution of terminal deoxynucleotidyl transferase (DNA nucleotidylexotransferase; nucleosidetriphosphate:DNA deoxynucleotidylexotransferase, EC 2.7.7.31) in thymocytes and peripheral lymphocytes from rat, mouse, and calf was studied by immunofluorescence using rabbit antiserum to homogeneous transferase from calf. Terminal transferase was readily detected in approximately 75% of cortical thymocytes, but not in medullary thymocytes or lymph node lymphocytes. The enzyme appeared to be present predominantly in the cytoplasm of positive thymocytes in ethanol-fixed cell smears and frozen sections. The reactivity of anti-terminal-transferase for thymocytes could be neutralized with purified calf enzyme. Results of experiments in which thymocytes were separated on 7-step discontinuous Ficoll density gradients suggested that cortical thymocytes are heterogeneous with respect to terminal deoxynucleotidyl transferase content.
Macromolecular factor VIII complex: functional and structural heterogeneity observed in von Willebrand swine with transfusion.
Authors: Griggs T R , Potter J S , McClanahan S B , Webster W P , Brinkhous K M
Published: May 2006

The physiologic activities concerned with hemostasis and associated with the Factor VIII macromolecular complex were investigated in swine with von Willebrand's disease after infusion of cryoprecipitate, a lyophilized Factor VIII concentrate, or porcine serum. Immediately after each infusion the various activities antihemophilic factor, von Willebrand platelet aggregating factor, and Factor VIII-related antigen, were elevated in approximate proportion to dose and the bleeding time was shortened.There was a late secondary rise in antihemophilic factor. During the period after infusion, there was a differential fall-off of the various activities, with the bleeding time effect lost first, followed by the von Willebrand platelet aggregating factor and then by the Factor VIII-related antigen. The plasma from swine with von Willebrand's disease late after infusion contained high levels of antihemophilic factor without other detectable activities of the complex. Antihemophilic factor, free of the other components, obtained from plasma from swine with von Willebrand's disease either before or late after infusion eluted from agarose gel columns both as high and lower molecular weight material, unlike normal antihemophilic factor, which had a high molecular weight. In contrast, on ultracentrifugation the antihemophilic factor in these plasma sedimented slowly, even though chromatographically the plasmas contained both high and low molecular weight factor. All of the Factor VIII complex activities in normal porcine plasma sedimented rapidly. These studies demonstrate the heterogeneity of the Factor VIII complex and the apparent dependence of its chromatographic and sedimentation behavior on the functional activities associated with the complex.
Reduction of collagen biosynthesis in blood vessels and other tissues by reserpine and hypophysectomy
Authors: Ooshima Akira , Fuller George C. , Cardinale George J. , Spector Sydney , Udenfriend Sidney
Published: May 2006

Synthesis of collagen in the vasculature and other tissues of normotensive rats is markedly reduced by reserpine. Hypophysectomy produces similar effects. The effects of reserpine on collagen biosynthesis may be mediated through the hypothalamus.
Identification of a protein related to tubulin in the postsynaptic density.
Authors: Feit H , Kelly P , Cotman C W
Published: May 2006

The postsynaptic density is a unique subcellular organelle associated with the synaptic complex and appears as an electron-dense area immediately subjacent to the postsynaptic plasma membrane. The postsynaptic density was isolated from the synaptosomal fraction and the protein constituents were analyzed by polyacrylamide gel electrophoresis. Polypeptides closely related to tubulin were identified as a major component of the postsynaptic density on the basis of molecular weight, subunit structure, and peptide map criteria.
In vitro synthesis and processing of a putative precursor for the small subunit of ribulose-1,5-bisphosphate carboxylase of Chlamydomonas reinhardtii.
Authors: Dobberstein B , Blobel G , Chua N H
Published: May 2006

Translation of polyadenylated mRNA of Chlamydomonas reinhardtii in a cell-free wheat germ system resulted in the synthesis of numerous discrete polypeptides. Among them was a species with molecular weight 20,000 that was immunoprecipitated specifically by antibodies raised against the authentic small subunit (16,500 daltons) of ribulose-1,5-bisphosphate carboxylase [3-phospho-D-glycerate carboxy-lyase(dimerizing), EC 4.1.1.39]. Since the immunoprecipitated polypeptide has a larger molecular weight by approximately 3500 than the small subunit (S) it was identified as a putative biosynthetic precursor (pS). Post-translational conversion of pS by a specific endoprotease yielded two detectable products: one apparently identical in size to S and the other, a small peptide, presumably representing the remainder of pS. The endoprotease requires sulfhydryl groups for its activity and is present in a C. reinhardtii postribosomal supernatant as well as in a free polysome fraction. The latter could account for the observation that completion of nascent chains in free polysomes yielded S but not pS. We propose that pS is an extrachloroplastic form of S and that the small peptide portion plays a role in the transfer of S into the chloroplast.
Natural human antibodies reactive with primate type-C viral antigens.
Authors: Kurth R , Teich N M , Weiss R , Oliver R T
Published: May 2006

A survey of human sera from healthy individuals revealed the presence of naturally occurring antibodies that react in radioimmunoprecipitation assays with proteins of mammalian type-C viruses. Of 39 sera tested, 100% showed reactivity against baboon endogenous virus, whereas only 49% showed reactivity against simian sarcoma-associated virus. Polyacrylamide gel electrophoresis of immune precipitates revealed one to three bands that comigrate with the virus structural proteins. There were low, but detectable, levels of antibody to the major internal protein of murine leukemia virus, but no activity against the structural proteins of avian sarcoma virus.
Characterization of polyoma virus T antigen.
Authors: Ito Y , Spurr N , Dulbecco R
Published: May 2006

High-titer antiserum raised in rats against the tumor (T) antigen of polyoma virus was used to purify the T antigen by the Staphylococcus protein A antibody adsorbent technique. Sodium dodecyl sulfate/polyacrylamide gel electrophoresis allowed the identification of a protein with an apparent molecular weight of 100,000-108,000 as a major component induced in lytically infected mouse cells. In cells infected by ts A mutants this component was temperature sensitive. Several minor components were also observed. In pulse and chase experiments there was a slight decrease in electrophoretic mobility of T antigen during the chase period at the permissive temperature, suggesting that the T antigen is a modified protein. In two lines of transformed cells, the amount of T antigen seemed to be considerably less than in lytically infected cells, but the size of the antigen appeared to be equal.
Dehydrogenase and transhydrogenase properties of the soluble NADH dehydrogenase of bovine heart mitochondria.
Authors: Hatefi Y , Galante Y M
Published: May 2006

The soluble NADH dehydrogenase of low molecular weight, isolated from complex I (NADH:ubiquinone oxidoreductase, EC 1.6.5.3) of the respiratory chain, has been shown to have NADPH dehydrogenase and NADPH leads to NAD transhydrogenase activities. Both activities are greatly increased in the presence of added guanidine-HCl and at pH values less than 6.5. The chromophores of the soluble enzyme (flavin and iron--sulfur centers) are reduced by NADH and NADPH to the same extent. The latter reduction is extremely slow, and is considerably stimulated in the presence of guanidine-HCl. The soluble dehydrogenase has little or no NADH leads to NADP and NADPH leads to NADP transhydrogenase activity. The former reaction is known to be energy-linked in submitochondrial particles; the latter was shown in the present studies also to be energy-linked. In view of the above and earlier results, possible mechanisms for dehydrogenation and transhydrogenation (nonenergy-linked and energy-linked) involving reduced and oxidized NAD and NADP are proposed.
Mapping of closed circular DNAs by cleavage with restriction endonucleases and calibration by agarose gel electrophoresis.
Authors: Parker R C , Watson R M , Vinograd J
Published: May 2006

The cleavage of DNA by restriction endonucleases can be limited by the addition of ethidium bromide. When closed circular DNA is used as a substrate, DNA with one-site cleavages of one or both strands can be made by adding appropriate amounts of dye. The singly cleaved DNA is a complete set of full-length permuted linear molecules. Fractionation of the products of a digestion of the permuted linears with a single-hitting restriction endonuclease by gel electrophoresis yields a series of bands that can be used to determine relative molecular weights of the DNA fragments in the gel without the introduction of standards. It is possible to determine the relative molecular weight of a fragment to within +/-2.5%. These molecular weights immediately allow the determination of the HindIII and Hpa I maps of simian virus 40. The HindIII map of bacteriophage PM2 was determined by this method with one ambiguity that was resolved by using traditional techniques.
Cleavage of Rous sarcoma viral polypeptide precursor into internal structural proteins in vitro involves viral protein p15.
Authors: von der Helm K
Published: May 2006

The polypeptide precursor pr76 to the internal viral group specific (gs) antigen proteins of Rous sarcoma virus, synthesized in a cell-free system of ascites cells, has been processed in vitro into the viral proteins by purified viral protein p15 as well as by disrupted Rous sarcoma virus. Disrupted Rauscher murine leukemia virus does not stimulate the cleavage process in vitro. Autocatalytic cleavage of the polypeptide precursor pr76 or Rous sarcoma virus, which contains the peptide sequence of p15, is not observed.
Regulation of hepatic nuclear guanylate cyclase.
Authors: Earp H S , Smith P , Huang Ong S H , Steiner A L
Published: May 2006

In immunohistochemical studies of rat liver tissue slices and purified nuclei, adenosine 3':5'-cyclic monophosphate (cAMP) and guanosine 3':5'-cyclic monophosphate (cGMP) immunofluorescence on the nuclear membrane are sequentially increased after glucagon administration. An explanation for the increased cGMP immunofluorescence was sought in experiments in which guanylate cyclase [GTP pyrophosphate-lyase (cyclizing), EC 4.6.1.2]activity of hepatic subcellular fractions was determined. The results showed that a nuclear guanylate cyclase exists which can be distinguished from the soluble and crude particulate guanylate cyclases. The activity of the nuclear enzyme was increased by 35% in nuclei isolated from rats 30 min after glucagon injection, the time at which maximal nuclear membrane cGMP immunofluorescence is observed. Because glucagon altered both cAMP location and levels prior to the observed changes in nuclear cGMP metabolism, the hypothesis that cAMP acted as the second messenger was tested. In vitro incubation of nuclei isolated from control rats with 10(-5) M cAMP produced a 25% increase in nuclear guanylate cyclase activity. With nuclei isolated from glucagon-treated rats, no significant increase in enzyme activity was observed; this indicates that maximal stimulation of nuclear guanylate cyclase by cAMP occurred at levels that are obtained in vivo after glucagon administration. These findings suggest that hepatic nuclear cGMP content may be regulated by a specific organelle guanylate cyclase and that cAMP may be one of the determinants of this enzyme's activity.
Three-dimensional structure of neurotoxin a from venom of the Philippines sea snake.
Authors: Tsernoglou D , Petsko G A
Published: May 2006

The crystal structure of neurotoxin a from the venom of Philippines sea snake Laticauda semifasciata has been determined at 2.5 A resolution by x-ray diffraction. Comparison with the structure of neurotoxin b from the same source indicates that the two toxins differ only by substitution at His 26. Earlier chemical work had suggested a difference in chain length and considerable differences in amino acid composition. The difference between our a and b toxins is the same as that reported from sequence analysis for the related erabutoxins a and b from Japanese sea snake, and suggests that the Philippines toxin may be identical to erabutoxin. The replacement of His 26 by a shorter side-chain in toxin a has no effect on the structure of the rest of the molecule. In particular, the protruding loop, which we believe interacts with the acetylcholine receptor, is not affected, even though His 26 is in the loop.
Relative conformational rigidity in oxytocin and (1-penicillamine)-oxytocin: a proposal for the relationship of conformational flexibility to peptide hormone agonism and antagonism.
Authors: Meraldi J P , Hruby V J , Brewster A I
Published: May 2006

A comparative study of the proton and carbon-13 nuclear magnetic resonance spectral parameters of the peptide hormone oxytocin and of its competitive inhibitor [1-L-penicillamine]oxytocin has been made, and the results analyzed in terms of comparative conformational and dynamic properties. The results indicate that oxytocin has a flexible conformation, while [1-L-penicillamine]oxytocin has a more restricted conformation. The results provide a framework for understanding the mechanism of peptide hormone agonism and antagonism for these compounds, and an approach for understanding some features of the interaction of the hormone and related compounds with their receptor.
In vitro biosynthesis of beta-endorphin in pituitary glands.
Authors: Crine P , Benjannet S , Seidah N G , Lis M , Chrétien M
Published: May 2006

beta-Endorphin is a 31 amino acid polypeptide isolated from the pituitary gland of different species of animals. It has strong morphine-like activity. It is formed of amino acid residues 61-91 of beta-lipotropin. Speculation has arisen whether it is biosynthesized in situ or transformed after secretion of beta-lipotropin. The present in vitro studies show that it is found as beta-endorphin in bovine pituitary slices incubated with radioactive amino acid precursor [35S]methionine. Chemical characterization and microsequencing of the newly biosynthesized material proves its identity with isolated unlabeled beta-endorphin and shows that it has a methionine residue at its fifth position, as expected.
Collagen degradation in rat skin but not in intestine during rapid growth: effect on collagen types I and III from skin.
Authors: Klein L , ChandraRajan J
Published: May 2006

Metabolic degradation of prelabeled collagen in whole body skin and whole intestine was compared to that of types I and III collagens from skin in young, rapidly growing rats. Pregnant rats were given [3H]proline during the last week of gestation; and after birth, littermates were compared. Between the second and sixth weeks of age, there was a 43% loss of radioactivity from dermal collagen but no significant loss of radioactivity from intestinal collagen. Pepsin treatment solubilized 90% of the dermal collagen but only 12% of intestinal collagen. Skin from 2- and 6-week-old rats yielded the same proportions of type I and type III collagens (type I, 82%; type III, 18%). The relative losses of total radioactivity from types I and III were similar to each other (50 and 44%, respectively) and to the loss from whole skin. Because types I and III collagens are known to be present in both skin and intestine, the marked degradation of both collagen types in skin but not in the intestine may be related to the amount and kind of intermolecular crosslinks present.
Replication of duplex DNA by bacteriophage T7 DNA polymerase and gene 4 protein is accompanied by hydrolysis of nucleoside 5'-triphosphates.
Authors: Kolodner R , Richardson C C
Published: May 2006

Homogeneous preparations of phage T7 gene 4 protein catalyze the hydrolysis of dNTPs and rNTPs to NDPs and Pi in the presence of single-stranded DNA. Synthesis on single-stranded DNA by T7 DNA polymerase (DNA nucleotidyltransferase; deoxynucleosidetriphosphate:DNA deoxynucleotidyltransferase, EC 2.7.7.7) does not affect the hydrolysis of NTPs by the gene 4 protein. Gene 4 protein does not catalyze the hydrolysis of NTPs in the presence of duplex DNA, nor can T7 DNA polymerase use duplex DNA as a template. However, the two proteins together can replicate duplex DNA and, under these conditions, synthesis is accompanied by hydrolysis of NTPs. During synthesis on duplex templates in the presence of T7 DNA polymerase, gene 4 protein, dNTPs, and rNTPs, 4.2 NTPs are hydrolyzed for each dNMP polymerized. 2'3'-Dideoxy-TTP, an inhibitor of DNA synthesis, inhibits hydrolysis by the gene 4 protein during synthesis on duplex DNA, and beta, gamma-methylene-dTTP, an inhibitor of hydrolysis by the gene 4 protein, stops DNA synthesis on duplex DNA. The multiple activities of gene 4 protein are shown to reside in a single protein molecule.
Higher-order structure of human mitotic chromosomes.
Authors: Bak A L , Zeuthen J , Crick F H
Published: May 2006

From observations on the partial disintegration of isolated human metaphase chromosomes we propose that human metaphase chromatids have a rather simple organization based on the folding and coiling of a long, regular, hollow cylindrical structure with a diameter of about 4000 A. This cylindrical structure, the unit fiber, is postulated to be a super-solenoid formed by the coiling of a 300 A solenoid, itself composed by coiling the basic string of nucleosomes. The structure of a human chromatid would thus be a hierarchy of helices, the contraction ratio of each coil, in ascending order of size, being approximately 7, 6, 40, and 5. This model appears to explain the estimated mass/unit length and accounts for many of the known features of human mitotic chromatids.
Two-dimensional analysis of flagellar proteins from wild-type and paralyzed mutants of Chlamydomonas reinhardtii.
Authors: Piperno G , Huang B , Luck D J
Published: May 2006

Flagellar polypeptides of Chlamydomonas reinhardtii were analyzed in two-dimensions by isoelectric focusing and electrophoresis in the presence of sodium dodecyl sulfate. In addition to flagellar tubulin, over 130 polypeptides were resolved and 100 of these were identified as axonemal components in wild-type organisms. Flagella of two nonconditional paralyzed mutants, pf 14 and pf 1, were also analyzed and, at the same time, electron microscopic studies were carried out. pf 14 flagella, which completely lack radial spokes and associated spokeheads, are missing 12 polypeptides. Six of these polypeptides are also missing from pf 1 flagella in which spokes are clearly present but spoke heads appear to be absent.
Host specificity of a serum marker for hepatitis B: evidence that "e antigen" has the properties of an immunoglobulin.
Authors: Neurath A R , Strick N
Published: May 2006

A family of antigens, referred to collectively as e antigen (eAg), has been detected in sera of some individuals with liver disease who test positive for hepatitis B surface antigen. Studies on eAg partially purified by affinity chromatography on insolubilized antibodies to eAg revealed the following: (i) eAg has the physicochemical and immunologic properties of an immunoglobulin, predominantly of the IgG4 subclass, and (ii) specific antigenic sites, designated as e determinants, differentiate eAg from other immunoglobulins. We suggest that these determinants represent idiotypic determinants on antibodies that are formed in response to hepatitis B virus infection and that block the host's immune surveillance mechanisms by which virus proliferation is stopped.
Involvement of histone H1 in the organization of the chromosome fiber.
Authors: Renz M , Nehls P , Hozier J
Published: May 2006

At high ionic strength (e.g., physiological salt concentrations) chromosome fibers are 200 A in diameter and composed of discrete globular structures that are held together by histone H1. At low ionic strength the fibers unfold and appear as the familiar chains of nucleosomes (80 A in diameter). The unfolding of chromosome fibers occurs within a narrow salt range. It results from a change in the mode of the interaction between histone H1 and the chromosome fiber and is very likely the consequence of a change from cooperative binding between histone H1 and DNA to a noncooperative binding. In the noncooperative binding state histone H1 molecules are randomly redistributed along the chromosome fiber.
Adenylate cyclase permanently uncoupled from hormone receptors in a novel variant of S49 mouse lymphoma cells.
Authors: Haga T , Ross E M , Anderson H J , Gilman A G
Published: May 2006

A novel variant of the S49 mouse lymphoma has been selected from wild-type cells by growth in medium containing the beta-adrenergic agonist terbutaline and inhibitors of cyclic nucleotide phosphodiesterase. In contrast to the situation in the wild-type clone, synthesis of adenosine 3':5'-monophosphate (cyclic AMP) is not stimulated by beta-adrenergic agonists or by prostaglandin E1 either in intact variant cells or in membrane preparations of such clones. However, basal and NaF-stimulated activities of adenylate cyclase [ATP pyrophosphate-lyase (cyclizine), EC 4.6.1.1] are normal, enzyme activity is stimulated by guanyl-5'-yl imidodiphosphate [Gpp(NH)p], and intact cells accumulate cyclic AMP when exposed to cholera toxin. Furthermore, variant cell membranes possess ligand-binding activity consistent with the conclusion that a normal or an excessive number of beta-adrenergic receptors is present. Thus, interaction between the hormone-binding and the catalytic moieties of the adenylate cyclase system is lost. This variant phenotype, designated as uncoupled (UNC), has been stable for more than 100 generations without exposure to the drugs used for selection. Such cells should be useful for the elucidation of methanisms of transmission of information from hormone receptors to adenylate cyclase.
Postulated deficiency of hepatic heme and repair by hematin infusions in the "inducible" hepatic porphyrias.
Authors: Watson C J , Pierach C A , Bossenmaier I , Cardinal R
Published: May 2006

There is compelling, indirect evidence of hepatic heme deficiency due primarily to the respective genetic errors of the three inducible hepatic porphyrias, acute intermittent porphyria, porphyria variegata, and hereditary coproporphyria. The induction is enhanced by exogenous inducers such as barbiturate, estrogens and other "porphyrogenic" chemicals and factors, including glucose deprivation. The newer knowledge of the induction of delta-aminolevulinic acid synthetase [delta-aminolevulinate synthase; succinyl--CoA:glycine C-succinyltransferase (decarboxylating), EC 2.3.1.37] in relation to inadequate heme, and repression by heme, stimulated early trials of hematin infusions to overcome the acute relapse in the foregoing inducible porphyrias. Recently this experience has been considerably expanded, 143 infusions of hematin having been given in 22 cases. Studies of the effect on the serum concentrations of delta-aminolevulinic acid and porphobilinogen have shown a highly significant decline, often to 0, especially of delta-aminolevulinic acid. A distinct relationship to the clinical severity of the attack has been evident in the frequency and magnitude of decline of serum delta-aminolevulinic acid and porphobilinogen. This was regularly associated with objective clinical improvement.
Quantum yields for oxygenic and anoxygenic photosynthesis in the cyanobacterium
Oscillatoria limnetica
Authors: Oren A. , Padan E. , Avron M.
Published: May 2006

A comparison of the quantum yield spectra of the oxygenic (H
2
O as the electron donor) with the anoxygenic (H
2
S as the electron donor) photosynthesis of the cyanobacterium,
Oscillatoria limnetica
reveals that anoxygenic photosynthesis is driven by photosystem I only. The highest quantum yields of the latter (maximum; 0.059 CO
2
molecules/quantum of absorbed light) were obtained with wavelengths which preferentially excite photosystem I (<550, >650) in which chlorophyll
a
and carotenoids are the major pigments. The addition of 3-(3,4-dichlorophenyl)-1,1-dimethylurea had no effect on anoxygenic photosynthesis, and no enhancement in quantum efficiency was observed by a superimposition of light preferentially exciting photosystem II.

Oxygenic photosynthesis efficiently utilizes only a narrow range of the absorption spectrum (550-650 nm) where light is provided in excess to photosystem II via phycocyanin. The quantum yield (0.033 CO
2
molecules/quantum of absorbed light) is lower than the theoretical yield by a factor of 3, possibly due to inefficient light transfer from photosystem II to I. Thus, 3-fold enhancement of oxygenic photosynthesis by superimposition of photosystem I light, and low quantum yields for anoxygenic photosynthesis, were obtained in this region. These results are consonant with the suggestion that such a cyanobacterium represents an intermediate stage in phototrophic evolution.
Perhydrohistrionicotoxin: a potential ligand for the ion conductance modulator of the acetylcholine receptor.
Authors: Eldefrawi A T , Eldefrawi M E , Albuquerque E X , Oliveira A C , Mansour N , Adler M , Daly J W , Brown G B , Burgermeister W , Witkop B
Published: May 2006

Histrionicotoxin from the Colombian frog Dendrobates histrionicus and its perhydro derivative reversibly block the acetylcholine-sensitive ion conductance system in frog neuromuscular preparations. The perhydro derivative and [3H]perhydrohistrionicotoxin, like histrionicotoxin, caused a significant decrease in the peak amplitude of the end-plate current and shortened its rise time and half-decay time. In membrane preparations from Torpedo electroplax, [3H]perhydrohistrionicotoxin bound reversibly to a limited number of high-affinity sites [dissociation constant, (KD) = 0.4 micronM]. The ratio of perhydrohistrionicotoxin to acetylcholine binding sites in these membrane preparations approached 2. Histrionicotoxins, local anesthetics, and certain cholinergic agonists inhibited binding of perhydrohistrionicotoxin. Binding of perhydrohistrionicotoxin to membranes was decreased by heat or treatment with proteases. Treatment of membranes with Triton X-100 solubilized acetylcholine binding proteins and apparently also perhydrohistrionicotoxin-binding proteins. However, the detergent Triton X-100 also bound [3H]perhydrohistrionicotoxin. This nonspecific binding was not saturable and complicated studies on the antagonism by drugs of binding of [3H]perhydrohistrionicotoxin. In solubilized preparations the binding protein for acetylcholine could be removed by affinity chromatography or immunoprecipitation without affecting binding of perhydrohistrionicotoxin. Sephadex chromatography also separated acetylcholine- from perhydrohistrionicotoxin-binding proteins. Perhydrohistrionicotoxin did not bind significantly to purified acetylcholine-receptor protein but presumably bound to an ion conductance modulator protein that was associated with the acetylcholine-receptor in intact membrane and readily separable from the receptor protein after solubilization.
Uncouplers and the molecular mechanism of uncoupling in mitochondria.
Authors: Kessler R J , Vande Zande H , Tyson C A , Blondin G A , Fairfield J , Glasser P , Green D E
Published: May 2006

Uncouplers are molecules with protonophoric and ionophoric capabilities that mediate coupled cyclical transport of cations--a transport that takes precedence over all other coupled processes. Uncouplers form cation-containing complexes with electrogenic ionophores that potentiate cyclical transport of cations. The molecular mechanism of uncoupling sheds strong light on the mechanism of coupling.
Interaction of cholinergic ligands and local anesthetics with plasma membrane fragments from lobster axon.
Authors: Marquis J K , Hilt D C , Papadeas V A , Mautner H G
Published: May 2006

Isologous local anesthetics containing the ester, thiolester, or selenolester grouping and their quaternary ammonium analogs were studied for their ability to displace [3H]nicotine from plasma membrane fragments of lobster nerve. Tertiary and quaternary analogs were equiactive. The relative ability of oxo, thio, and seleno analogs to displace nicotine was the same as their relative ability to block axonal conduction and synaptic transmission. Among cholinergic ligands, choline and aminocholine, previously shown to be inactive as depolarizing agents, were uniquely unable to displace nicotine. The findings are compatible with the presence of a biopolymer capable of binding cholinergic ligands in axonal membranes and support the postulate that the relative inactivity of quaternary compounds in intact axons is due to permeability barriers.
The complete amino acid sequence of prochymosin.
Authors: Foltmann B , Pedersen V B , Jacobsen H , Kauffman D , Wybrandt G
Published: May 2006

The total sequence of 365 amino acid residues in bovine prochymosin is presented. Alignment with the amino acid sequence of porcine pepsinogen shows that 204 amino acid residues are common to the two zymogens. Further comparison and alignment with the amino acid sequence of penicillopepsin shows that 66 residues are located at identical positions in all three proteases. The three enzymes belong to a large group of proteases with two aspartate residues in the active center. This group forms a family derived from one common ancestor.
Effect of uridine on cellular UTP and glycogen synthesis in skeletal muscle: stimulation of UTP formation by insulin.
Authors: Haugaard E S , Frantz K B , Haugaard N
Published: May 2006

The relation between cellular uracil nucleotides and ability to synthesize glycogen was studied in rat diaphragm incubated in vitro. In the absence of exogenous uridine the tissue content of UTP and rate of glycogen synthesis decreased with time. Uridine added to the medium increased cellular UTP and UDPG and stimulated glycogen synthesis. Insulin significantly increased the synthesis of UTP from extracellular uridine. This action of insulin appeared to be due to a stimulation of phosphorylation of the nucleoside and not to an effect on transport at the concentrations of uridine studied. However, an effect of insulin on transport of uridine at low concentrations cannot be excluded.
Pregrowth hormone messenger RNA: glucocorticoid induction and identification in rat pituitary cells.
Authors: Tushinski R J , Sussman P M , Yu L Y , Bancroft F C
Published: May 2006

We have investigated whether the large (5- to 15-fold) stimulation of synthesis of growth hormone (somatotropin) observed upon exposure of a strain of rat pituitary (GH3) cells to dexamethasone (a synthetic glucocorticoid) arises from a stimulation of pregrowth hormone mRNA. A good agreement was observed between the stimulation of growth hormone synthesis and the stimulation of cytoplasmic levels of pregrowth hormone mRNA, assayed by translation in wheat germ extracts. Electrophoresis on formamide-acrylamide gels of oligo(dT)-treated membrane fraction RNA revealed a band that was induced by dexamethasone to about the same extent as was translatable pregrowth hormone mRNA. Elution of the band and translation in wheat germ extracts showed directly that it contained pregrowth hormone mRNA. These results suggest that the dexamethasone induction of growth hormone synthesis in GH3 cells arises from an accumulation of pregrowth hormone mRNA in the cytoplasm of the cells. The pregrowth hormone mRNA band observed by gel electrophoresis had an estimated molecular weight of 3.6 X 10(5), suggesting the existence in this molecule of an untranslated region at least 200 nucleotides in length.
Effect of medium composition on protein degradation and DNA synthesis in rat embryo fibroblasts.
Authors: Warburton M J , Poole B
Published: May 2006

Fibroblasts in medium deficient in serum, amino acids, phosphate, or glucose stop synthesizing DNA and increase the rate of degradation of their long-lived cellular proteins approximately 2-fold. There is no difference in the rate of degradation of short-lived proteins under these conditions. Insulin, dexamethasone, and fibroblast growth factor act synergistically to inhibit protein degradation and to stimulate thymidine incorporation to about the same extent as serum. When the medium content in serum or fibroblast growth factor is varied over a wide range, there is a close, inverse correlation between the rate of protein degradation and the extent of thymidine incorporation. When serum is added to cells that have been deprived of serum, the inhibition of protein degradation is immediate whereas the enhanced rate of protein degradation in serum-free medium is attained within 1 hr after serum removal. A 30-min exposure to serum followed by incubation in serum-free medium was as effective as continuous exposure to serum in stimulating thymidine incorporation after 8-24 hr.
Cell surface-associated structural proteins in connective tissue cells.
Authors: Bornstein P , Ash J F
Published: May 2006

Collagen and/or procollagen was demonstrated on the surface of monolayers of fibroblasts from normal rat kidney by indirect immunofluorescence with affinity-purified antibodies to collagen. The protein was arrayed in a reticular fashion on the cell surface and, in cells attached to a substratum, was severely restricted in its ability to undergo antibody-induced translational movement in the plane of the membrane. A similar pattern was observed for fibronectin (LETS protein, fibroblast surface antigen). These macromolecules were lost when fibroblasts were dissociated and examined in suspension cultures and were not regained until after the cells were replated. On the basis of the morphological findings, and in view of the likelihood of an interaction between fibronectin and collagen, we propose that these that these proteins form a meshwork on the cell surface. This external protein meshwork may mediate a number of important cellular functions, including attachment to a substratum and other interactions with the extracellular matrix.
Visualization of a system of filaments 7-10 nm thick in cultured cells of an epithelioid line (Pt K2) by immunofluorescence microscopy.
Authors: Osborn M , Franke W W , Weber K
Published: May 2006

During our studies with antibodies against structural proteins of the cytoskeleton of eukaryotic cells we have observed that sera from many normal rabbits decorate a fiber system in cells of the established rat kangaroo cell line Pt K2. The display and organization of these fibers are different from those of microfilament bundles (decorated by antibody to actin) and microtubules (decorated by antibody to tubulin). This new fiber system can be further distinguished by its resistance to reorganization when cells are treated with Colcemid or cytochalasin B. The decoration of this fiber system is not detected if Pt K2 cells are fixed with formaldehyde. Such sera also appear to decorate swirls of perinuclear fibers in mouse Neuro 2a cells, and in mouse 3T3 cells treated with mitotic drugs. Comparison of the immunofluorescence pictures with electron microscopic data suggests that the sera are visualizing bundles of intermediate 7- to 10-nm filaments.
General variational principles applicable to the hybrid element method
Authors: Herrera Ismael
Published: May 2006

Functional valued operators are used to formulate diffraction problems in a general abstract form. Variational principles for this formulation are developed. They are then applied to derive results on the linearized theory of free surface flows previously reported. Applications are also made to potential theory and elasticity.
Magnetic properties and structure of oxyhemoglobin.
Authors: Pauling L
Published: May 2006

A review of the published evidence reinforces the conclusion reached by Pauling and Coryell in 1936 (Proc. Natl. Acad. Sci. USA 22, 210-216) that oxyhemoglobin in blood or in solution at 20 degrees has zero magnetic moment and fails to support a recent contradictory suggestion based on magnetic susceptibility of frozen samples at temperatures below 250 K. Predicted values of bond lengths and bound angles for carbonmonoxyhemoglobin and oxyhemoglobin are given.
Model for “charge-relay”: Acceleration by carboxylate anion in intramolecular general base-catalyzed ester hydrolysis by the imidazolyl group
Authors: Komiyama Makoto , Bender Myron L. , Utaka Masanori , Takeda Akira
Published: May 2006

The effect of benzoate anion on intramolecular general base-catalyzed ester hydrolysis by the imidazolyl group in
endo
-5-[4′(5′)-imidazolyl]bicyclo[2.2.1]hept-
endo
-2-yl
trans
-cinnamate was examined in dioxane/H
2
O solutions. Benzoate anion exhibited a remarkable acceleration of the intramolecular general base-catalyzed hydrolysis of
endo
-5-[4′(5′)-imidazolyl]bicyclo[2.2.1]hept-
endo
-2-yl
trans
-cinnamate by the imidazolyl group. The rate of hydrolysis in the presence of the benzoate anion increased with the dioxane mole fraction and was proportional to the concentration of benzoate anion. On the other hand, the rate of hydrolysis of
endo
-5-[4′(5′)-imidazolyl]bicyclo[2.2.1]hept-
endo
-2-yl
trans
-cinnamate in the absence of benzoate anion decreased with the dioxane mole fraction. Thus, the ratio of the rate in the presence of benzoate anion to that in the absence of benzoate anion drastically increased with the dioxane mole fraction and attained a 2500-fold rate acceleration at a dioxane mole fraction of 0.42 (the highest experimentally attainable) when the concentration of benzoate anion was 0.5 M. The proposed mechanism involves proton abstraction by the benzoate anion from the imidazolyl group, followed by proton abstraction by the imidazolyl group from H
2
O, resulting in effective general base-catalysis of hydrolysis. The results of the present paper provide support for the “charge-relay” system in serine proteases.
1976 bedload measurements, East Fork River, Wyoming
Authors: Leopold Luna B. , Emmett William W.
Published: May 2006

Quantitative measurements of bedload-transport rate in the East Fork River, Wyoming, show large spatial and temporal variabilities in traction load. The standard deviation for 1-min increments of the mean transport rate is commonly 50-100% of the mean transport rate. The transport rates measured individually over eight equal-length increments of channel width indicate greater than 10-fold variations in transport rates from subwidth sections of minimum transport to subwidth sections of maximum transport.
Loss of infectivity of brome mosaic virus RNA after chemical modification of the 3' or 5' terminus.
Authors: Kohl R J , Hall T C
Published: May 2006

Brome mosaic virus (BMV) RNA that had both termini chemically modified by periodate oxidation and aniline-catalyzed cleavage of the terminal nucleotide had drastically reduced infectivity. BMV RNA that was first enzymatically tyrosylated to protect the 3' terminus from modification, and then modified at the 5' terminus by periodate oxidation and aniline cleavage, had a similar reduction in infectivity. Tyrosylation followed by acetylation modifies only the 3' terminus. Nevertheless, acetylated tyrosyl-BMV RNA was less than one-fourth as infectious as a control sample subjected to procedures that differed only by the presence of tyrosinol (which prevents aminoacylation and subsequent acetylation). For each modified form of viral RNA, care was taken to test the infectivity of appropriate control samples. The integrity of the modified RNAs was examined by gel electrophoresis and by biological translation and aminoacylation assays. We conclude that, in different ways, both the 5'- and 3'-terminal structures of BMV RNA play important roles during infection of the host.