bluuebunny/crossref_metadata_2025 huggingface dataset:
Tissue interaction in androgen response of embryonic mammary rudiment of mouse: identification of target tissue for testosterone.
Authors: Kratochwil K , Schwartz P
Published: May 2006

In the androgen response of the embryonic mammary rudiment of the mouse, both gland epithelium and surrounding mesenchyme are visibly involved. The question whether this is due to a direct action of testosterone on both tissues was investigated in experimental combination of mammary epithelium and mammary mesenchyme, derived either from normal or from androgen-insensitive (XTfm/Y) embryos. A typical androgen response occurred in combinations of androgen-insensitive epithelium with normal mesenchyme, whereas all combinations of normal epithelium with androgen-insensitive mesenchyme failed to respond. It is therefore concluded that only the mesenchyme of the mammary rudiment is the target tissue for testosterone, and that all changes in the gland epithelium, including its necrosis, are secondarily caused by testosterone-activated mesenchymal cells.
Clustering and endocytosis of membrane receptors can be induced in mature erythrocytes of neonatal but not adult humans.
Authors: Schekman R , Singer S J
Published: May 2006

Concanavalin A (Con A) is taken up by endocytosis in mature erythrocytes of newborn humans but not in adult red cells. Thin sections of neonatal cells incubated with ferritin-conjugated Con A at 37 degrees show ferritin clusters on invaginations at the surface and in intracellular vesicles, but such invaginations and vesicles are absent with adult cells. The endocytosis induced by ferritin-conjugated Con A is inhibited at 0 degrees, and by methyl-alpha-D-mannopyranoside at 37 degrees. Succinylation of Con A, which is known to convert it from the tetrameric to dimeric form, renders Con A inactive in cell agglutination and endocytotic vesicle formation, presumably by reducing the number of oligosaccharide chains simultaneously bound by a single Con A molecule. Ferritin-conjugated succinyl Con A binds to neonatal erythrocytes but does not induce endocytosis; if, however, antibodies to ferritin are now added, endocytosis occurs. These results are consistent with a greater lateral mobility of at least a fraction of Con A recptors in the membrane of the intact neonatal erythrocyte compared to the adult. The results also support the hypothesis that the clustering of receptors is obligatory for endocytosis to occur. No discernible difference was found in the sodium dodecyl sulfate/polyacrylamide gel patterns of the membrane proteins of the neonatal and adult cells.
Repair tracts in mismatched DNA heteroduplexes.
Authors: Wagner R , Meselson M
Published: May 2006

Heteroduplexes with mismatches at four sites were constructed from separated strands of lambda DNA and used to transfect Escherichia coli under recombinationless conditions. The output phages from 967 single cells in one experiment and 1016 in another were analyzed to determine the pattern of mismatch repair. A wide range of repair frequencies was found among the mismatches studied. Repair involving two or more close sites in the same heteroduplex occurs much more often on thesamestrandthanonopposite strands.Analysis of the pattern of repair suggeststhat repair tracts initiate at mismatches, propagate preferentially in the 5'leads to 3' direction, and extend an average distance of ca 3000 nucleotides.
Covalently linked chlorophyll
a
dimer: A biomimetic model of special pair chlorophyll
Authors: Wasielewski Michael R. , Studier Martin H. , Katz Joseph J.
Published: May 2006

The synthesis of a covalent dimer of chlorophyll
a
which possesses properties strikingly similar to those exhibited by P700 special pair chlorophyll
in vivo
is described. The covalent dimer is characterized by several spectroscopic techniques. Hydrogen bonding nucleophiles, such as water, primary alcohols, and primary thiols, are effective in generating a species from solutions of 10 μM covalent dimer in hydrophobic solvents which absorbs light near 700 nm. Formation of this
in vitro
special pair is a rapid, spontaneous process at room temperature. The range of nucleophiles which promote this process suggests that amino acid residues may function in a similar fashion to form P700 in chlorophyll-protein complexes. The photochemical properties of this
in vitro
special pair mimic those of
in vivo
P700 species. The 697 nm absorption of the
in vitro
special pair undergoes photo-bleaching rapidly in the presence of iodine that results in the production of a cation radical which exhibits an electron spin resonance signal similar to that of oxidized P700 observed in
Chlorella vulgaris
.
Immunological characterization of the subunit of the 100 A filaments from muscle cells.
Authors: Lazarides E , Hubbard B D
Published: May 2006

We report the immunological characterization of the subunit of the intermediate sized (100 A) filaments from muscle cells. The protein as isolated from smooth muscle (chicken gizzard) has an apparent molecular weight of 50,000. It is insoluble in buffers that solubilize myosin and the majority of actin, but becomes soluble in the presence of urea. Under a variety of experimental conditions, that include the presence of 8 M urea, this new protein comigrates with actin during purification studies. The two proteins can be separated from each other by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, and antibodies have been elicited against the 50,000 dalton protein purified by using this technique. These antibodies crossreact with the partially purified protein in urea, but show no detectable cross reaction with actin or myosin. Indirect immunofluorescence reveals that in skeletal muscle this protein is found in close association with the Z lines of the sarcomeres and extends between the Z lines of adjacent myofibrils; it is also associated with filamentous structures that run along the length of a muscle fiber both in close association with the plasma membrane and between myofibrils at the level of their Z lines. In heart muscle, the protein shows the same distribution as in skeletal muscle. In addition, it is found intimately associated with intercalated disks and areas of membrane interaction between laterally associated heart muscle cells. The immunofluorescent localization to the subunit of the 100 A filaments suggests that in muscle cells this molecule may serve to link actin filaments at the level of the Z line (or intercalated disk) with the muscle plasma membrane. We believe that it functions in muscle primarily as a three dimensional matrix which interconnects individual myofibrils to one another and to the plasma membrane at the level of their Z lines. In this manner, this molecule may provide a framework that mechanically integrates all the contractile myofilaments during the contraction and relaxation of muscle. As a means of indicating its linking role in muscle, we have termed the protein desmin (from the Greek delta epsilon sigma mu os = link, bond).
Change in membrane potential during bacterial chemotaxis.
Authors: Szmelcman S , Adler J
Published: May 2006

To find out if there are changes in membrane potential during bacterial chemotaxis, we measured the membrane potential of Escherichia coli indirectly by use of the permeating, lipid-soluble cation triphenylmethylphosphonium. Addition of attractants or repellents to the bacteria brought about a hyperpolarizing peak (as well as additional, later changes in membrane potential). This peak was shown to be a part of the chemotactic mechanism based on the following evidence: (i) All attractants and repellents tested gave this peak while chemotactically inert chemicals did not. (ii) Mutants lacking galactose taxis failed to give the peak with galactose but did with another attractant and with repellents. (iii) Methionine, required for chemotaxis, is also required for production of this peak. (iv) A mutant in a control gene )flaI), unable to synthesize flagella and cytoplasmic membrane proteins related to motility and chemotaxis, failed to give the peak. (v) Paralyzed (mot) mutants gave little or none of the peak. Generally nonchemotactic (che) mutants, on the other hand, did give this peak. Very likely there are ion fluxes that bring about this change in membrane potential. We discuss the possible role of the mot gene product as an ion gate controlled by a methylation-demethylation process in response to attractants and repellents acting through their chemoreceptors.
Cellulose biosynthesis in Acetobacter xylinum: visualization of the site of synthesis and direct measurement of the in vivo process.
Authors: Brown R M , Willison J H , Richardson C L
Published: May 2006

In vivo synthesis of cellulose by Acetobacter xylinum was monitored by darkfield light microscopy. Cellulose is synthesized in the form of a ribbon projecting from the pole of the bacterial rod. The ribbon elongates at a rate of 2 mum min-1. The ribbon consists of approximately 46 microfibrils which average 1.6 X 5.8 nm in cross section. The observed microfibrillar elongation rate corresponds to 470 amol of glucose/cell per hr assimilated into cellulose. Electron microscopy of the process using negative staining, sectioning, and freeze-etching indicated the presence of approximately 50 individual synthetic sites organized in a row along the longitudinal axis of the bacterial rod and in close association with the outer envelope. The process of cellulose synthesis in Acetobacter is compared with that in eukaryotic plant cells.
Identification of biological molecules in situ at high resolution via the fluorescence excited by a scanning electron beam.
Authors: Hough P V , McKinney W R , Ledbeter M C , Pollack R E , Moos H W
Published: May 2006

Proteins, nucleic acids, and fluorescein-conjugated antibody are shown to be identifidable in situ via the fluorescence excited by the focused electron beam of a canning electron microscope. A molecular species is identified by its characteristic fluorescence spectrum and by a characteristic alteration of the spectrum with time under the electron beam. Primary protein fluorescence is relatively rapidly destroyed by the beam, but protein photoproduct fluorescence is more rugged and will in some cases permit detection of small numbers of protein molecules. Nucleic acid fluorescence is extremely long-lived and will permit detection of small numbers of nucleic acid residues. The theoretical resolution limit for localization of a particular molecular species -- about 20 A--is determined by the known maximum distance for molecular excitation by fast electrons. Drect extapolation from an observed resolution of 900 A in the localization of nucleic acid using a low-efficiency detector leads to an experimental resolution limit of less than 60 A. Fluorescence is strongly quenched by residual water in the specimen. Similar quenching is produced by some macromolecular associations and so may serve to localize such associations.
Cyclic nucleotide metabolism in compensatory renal hypertrophy and neonatal kidney growth.
Authors: Schlondorff D , Weber H
Published: May 2006

Cyclic nucleotide metabolism was investigated in growing kidneys of rats during compensatory hypertrophy and during neonatal development. After unilateral nephrectomy a mild and short-lasting decrease in cyclic 3':5" adenosine monophosphate (cAMP) was observed in the hypertrophying kidney. In contrast, cyclic 3':5' guanosine monophosphate (cGMP) showed a sharp decline to 20% of control at 15 min and a rapid rise to 200-300% above base-line at 1-72 hr. The alterations in renal tissue levels of cGMP were associated with parallel changes in the soluble, 100,000 X g supernatant guanylate cyclase activity [GTP pyrophosphate-lyase (cyclizing): EC 4.6.1.2]. No change was observed in total cGMP phosphodiesterase (3':5'-cyclic-nucleotide 5'-nucleotidohydrolase; EC 3.1.4.17). In the rapidly growing kidney of newborn rats cAMP levels were 983 +/- 65 and 833 +/- 42 pmol/g of kidney at 4 and 7 days after birth, and increased to adult levels (1518 +/- 57 pmol/g) at 21 days whereas cGMP levels were 59.8 +/- 6.8 and 92.5 +/- 13.9 pmol/g at 4 and 7 days and decreased to adult levels (36 +/- 1.5) at 21 days. The results indicate that compensatory renal hypertrophy and neonatal kidney growth are associated with changes in cAMP and cGMP metabolism.
Biochemistry of the filaments of brain.
Authors: Yen S H , Dahl D , Schachner M , Shelanski M L
Published: May 2006

Intermediate filaments-cytoplasmic filaments with a diameter of 8-9 nm-have been described in a large variety of cell types. In this study, the subunit protein of the neurofilament and the presumptive subunit of the astroglial filament are compared by immunological and biochemical methods and are found to be very similar. Strong crossreactions are also found between these proteins in a variety of mammalian species. These results suggest that the intermediate filaments may, like microtubules and microfilaments, represent a highly conserved and widely distributed fibrous protein system.
Parietal eye of the lizard: neuronal photoresponses and feedback from the pineal gland.
Authors: Engbretson G A , Lent C M
Published: May 2006

The parietal eye of the lizard responds to illumination by sending afferent impulses to the pineal gland during daylight, the photophase. The pineal gland has efferently conducting neurons which are especially sensitive to norepinephrine and whose feedback to the parietal eye enhances its photo responsiveness. During the scotophase, at night, the eye generates afferent impulses to the cessation of light and the pineal efferents are most sensitive to serotonin. Thus, the photo-and chemoresponses of this system of interacting neurons are nearly reversed during the two phases of the daily photoperiod of the lizard.
Androgen insensitivity in man: evidence for genetic heterogeneity.
Authors: Amrhein J A , Meyer W J , Jones H W , Migeon C J
Published: May 2006

We have studied ten phenotypically similar patients with complete androgen insensitivity. All of the patients tested had significantly elevated serum luteinizing hormone and plasma androgens within or above the normal adult male range. On the basis of specific dihydrotestosterone binding by skin fibroblasts, we identified two subgroups. Six patients from five different families had undetectable dihydrotestosterone binding, while four patients from two families had normal binding activity. Our results indicate that within the clinical syndrome of androgen insensitivity there are at least two distinct genetic variants. These variants may result from allelic mutations of the same X-linked gene specifying the dihydrotestosterone receptor or, alternatively, from mutations of separate genes both being essential for androgen action in responsive cells.
Superinfection epithelial nasopharyngeal carcinoma cells with Epstein-Barr virus.
Authors: Glaser R , de Thé G , Lenoir G , Ho J H
Published: May 2006

Attempts were made to superinfect epithelial explant cell cultures prepared from nasopharyngeal carcinomas with Epstein-Barr virus. Virus-specific markers were observed in such cultures 3 days after superinfection. In addition, expression of Epstein-Barr virus early antigens was observed in epithelial cell explant cultures treated with iododeoxyuridine. The results suggest that epithelial cells of at least certain nasopharyngeal carcinomas possess the receptor for the Epstein-Barr virus and that the latent virus genome can be induced from epithelial cells prepared from such tumors.
Acquisition of substrate-specific parameters during the catalytic reaction of penicillinase.
Authors: Citri N , Samuni A , Zyk N
Published: May 2006

The progress of the catalytic reaction of penicillinase (EC 3.5.2.6; penicillin amido-beta-lactamhydrolase) depends on the structure of the side-chain in derivatives of 6-aminopenicillanic acid (the parent substrate). Side-chains of one class promote the rate of the reaction and cause no deviation from the linear kinetics observed with the parent compound. By contrast, side-chains of the other class induce a time-dependent, reversible change in the parameters of the catalytic reaction. The rate decelerates considerably and then becomes constant; the decrease in kcat is accompanied by a corresponding decrease in Km. The initial parameters of the biphasic reaction, determined by stopped-flow spectrophotometry, approach those of the unsubstituted 6-aminopenicillanic acid. The final parameters, which are specific for each derivative, are not acquired when the native conformation of the enzyme is stabilized by homologous antibodies.
Specific positions involved in enzyme catalyzed covalent binding of benzo[a]pyrene to poly(G).
Authors: Meehan T , Warshawsky D , Calvin M
Published: May 2006

Covalent binding of benzo[a]pyrene to poly(G) was studied with the use of a radioactive assay and specifically labeled substrates to define the role of the 1, 3- and 6-positions of the hydrocarbon during this process. Binding was shown to be dependent on microsomes, NADPH, O2 and poly(G). 7, 8-Benzoflavone and 2', 2'-diethylaminoethyl-2, 2-diphenyl valerate were inhibitory w.hereas modulators of epoxide hydrase activity had little effect. 3H and 14C studies suggested a possible loss of one to two protons. Incorporation of [6-3H1]benzo[a]pyrene provided evidence that the 6-position of the hydrocarbon was not metabolized during covalent attachment to poly(G) and, furthermore, results with [1, 3, 6-3H]benzo[a]pyrene suggest that the 1- and 3-positions may not be involved either. After scaling up of the standard assay 20-fold, characterization of the tritiated BaP-poly(G) complex was carried out by hydrolysis and subsequent chromatography. Thin-layer chromatography of the isolated hydrolysis products treated with HCl or alkaline phosphatase indicated that the complex formed between BaP and poly(G) was covalently linked and composed of hydrocarbon-nucleotide(s).
Reconstitution of Qbeta RNA replicase from a covalently bonded elongation factor Tu-Ts complex.
Authors: Brown S , Blumenthal T
Published: May 2006

Escherichia coli phage Qbeta RNA replicase, an RNA-dependent RNA polymerase (RNA-dependent RNA nucleotidyltransferase), is a tetramer composed of one phage-coded polypeptide and three host-supplied polypeptides which are known to function in the biosynthesis of proteins in the uninfected host. Two of these polypeptides, protein synthesis elongation factors EF-Tu and EF-Ts, can be covalently crosslinked with dimethyl suberimidate to form a complex which lacks the ability to catalyze the known host functions catalyzed by the individual elongation factors. Using a previously developed reconstitution system we have examined the effects of crosslinking the EF-Tu-Ts complex on reconstituted replicase activity. Renaturation is significantly more efficient when exogenously added native EF-Tu-Ts is crosslinked than when it is not. Crosslinked EF-Tu-Ts can be purified from a crude crosslinked postribosomal supernatant by its ability to replace EF-Tu and EF-Ts in the renaturation of denatured Qbeta replicase. A sample of Qbeta replicase with crosslinked EF-Tu-Ts replacing the individual elongation factors was prepared. Although it lacked EF-Tu and EF-Ts activities, it could initiate transcription of both poly(C) and Qbeta RNA normally and had approximately the same specific activity as control enzyme. Denatured Qbeta replicase formed with crosslinked EF-Tu-Ts was found to renature much more rapidly than untreated enzyme and, in contrast to normal replicase, its renaturation was not inhibited by GDP. The results demonstrate that EF-Tu and EF-Ts function as complex in Qbeta replicase and do not perform their known protein biosynthetic function in the RNA synthetic reaction.
Isolation and structure of an untriakontapeptide with opiate activity from camel pituitary glands.
Authors: Li C H , Chung D
Published: May 2006

The isolation of an untriakontapeptide from camel pituitary extracts has been described. Its structure has been determined and shown to be identical to the sequence of carboxyl-terminal 31 amino acids of ovine beta-lipotropin. The peptide possesses very low lipotropic activity but significant opiate activity.
Cell surface protein partially restores morphology, adhesiveness, and contact inhibition of movement to transformed fibroblasts.
Authors: Yamada K M , Yamada S S , Pastan I
Published: May 2006

We have isolated the major cell surface glycoprotein of chick embryo fibroblasts, CSP, and added it to a variety of transformed cells in vitro. The transformed cells become more elongated, often more flattened, and show increased adhesion to the substratum. Several transformed cell lines also align in striking parallel arrays. This alignment is characterized by a decrease in the amount of nuclear overlapping, probably indicating restoration of contact inhibition of movement. The morphological changes are antagonized by antibody to CSP. These effects of CSP are not associated with an elevation of cellular 3':5'-cyclic AMP. Moreover, the morphological reversion is not accompanied by an alteration in growth properties. Our results are consistent with a role for CSP in cell adhesion and morphology but not in growth control.
Interferon treatment of mice: enhanced expression of histocompatibility antigens on lymphoid cells.
Authors: Lindahl P , Gresser I , Leary P , Tovey M
Published: May 2006

Treatment of young and mature mice with potent mouse interferon preparations results in a marked enhancement of the expression of histocompatibility antigens on the surface of thymocytes and splenic lymphocytes as measured by an enhanced absorption of alloantiserum. We postulate that such modifications of the cell surface may reflect an effect of interferon on lymphocyte maturation and may be relevant to the effect of interferon on lymphocyte function.
Thermodynamic studies of polymerization of deoxygenated sickle cell hemoglobin.
Authors: Magdoff-Fairchild B , Poillon W N , Li T , Bertles J F
Published: May 2006

Solubilities of deoxygenated sickle cell hemoglobin (deoxy-Hb S), at varying pH and temperature over a range of concentrations encompassing those found in erythrocytes, were measured. The technique involved ultracentrifugation, which gave values of the supernatant concentration and the mass of the sedimented material. The data establish that the solubility of doexy-Hb S is the saturation concentration and is independent of initial concentration. The mass of the pellet phase increases linearly with initial concentration. Moreover, the saturation concentration represents the critical concentration above which monomers are in equilibrium with polymers. These polymers are the putative cause of erythrocytes deformation associated with sickle cell anemia. The solubility-pH profiles of deoxy-Hb S at various temperatures, unlike those of other proteins, show no minima at the isoelectric pH but instead show a marked decrease in solubility below pH 7.0, indicating the predominance of polymerization over the expected increase in solubility. Deoxy-Hb S, within specified ranges of temperature and pH, possesses a negative temperature coefficient of solubility, a property characteristic of hydrophobic interactions. The saturation concentration is, however, temperature independent at conditions close to physiological. The enthalpy of polymerization (3.5 kcal/mol) is temperature independent from 6 degrees to 22 degrees for all pH values between 6.45 and 7.40. In the range of 22 degrees to 38 degrees, this parameter becomes less endothermic, having a value of 2.5 kcal/mol at pH 6.45 and a value of zero at pH 7.20. Such behavior of the system suggests a phase transition near 22 degreas. Within the range of conditions examined the polymerization is entropically driven.
Molecular cloning of DNA fragments produced by restriction endonucleases Sa1I and BamI.
Authors: Hamer D H , Thomas C A
Published: May 2006

The highly specific restriction endonucleases Sa1I and BamI produce DNA fragments with complementary, cohesive termini that can be covalently joined by DNA ligase. The Escherichia coli kanamycin resistance factor pML21 has one SalI site, at which DNA can be inserted without interfering with the expression of drug resistance or replication of the plasmid. A more convenient cloning vehicle can be made with the tetracycline resistance factor pSC101, since insertion of DNA either at its single site for Sa1I or at that for BamI inactivates plasmid-specified drug resistance but not replication. To take advantage of this insertional inactivation, pSC101 was joined to a Co1E1-ampicillin resistance plasmid having no Sa1I site, and to a Co1E1-kanamycin resistance plasmid having no BamI site. Chimeras formed with the resulting hybrid vehicles can be identified simply by replica plating. These three vehicles, which all replicate under relaxed control, have been used to clone and amplify Drosophila melanogaster DNA fragments.
Presence of messenger specifying sequences in the DNA of chromatin subunits.
Authors: Tien Kuo M , Sahasrabuddhe C G , Saunders G F
Published: May 2006

Messenger-specifying sequences in subunits of human lymphocyte chromatin were detected by hybridization of DNA complementary to cytoplasmic polyadenylylated RNA with DNA isolated from the subunits. Comparison of the kinetics and extents of hybridization of complementary DNA with chromatin subunit DNA and with nuclear DNA showed that most of the repetitive sequences and single copy sequences in mRNA are present in chromatin subunits. This result indicates that inclusion of a DNA sequence into the subunit does not prevent its transcription in vivo.
Unequal accumulation of alpha- and beta-globin mRNA in erythropoietic mouse spleen.
Authors: Cheng T C , Kazazian H H
Published: May 2006

Relative amounts and rates of synthesis of alpha- and beta-globin mRNAs were determined during splenic erythropoiesis in mice. At times after injection of mice with phenylhydrazine, alpha- and beta-globin mRNAs were separated by gel electrophoresis and quantitated by densitometric scanning of stained gels. At 66 hr after injection, the ratio of beta to alpha mRNA is about 1.2. By 138 hr, total globin mRNA is 5-fold greater in spleen cells, and the beta to alpha mRNA ratio approaches 2. This ratio remains around 1 in reticulocytes throughout this period. Analyses of globin products directed by these mRNAs from spleen cells and reticulocytes in the ascites cell-free system reflect the beta to alpha mRNA ratio observed by electrophoresis. Relative rates of synthesis of globin mRNAs were estimated after incubation of spleen cells with either [3H] uridine or [3H] adenosine. Although synthesis of both mRNAs is maximal at 114 hr and then declines sharply, beta mRNA is synthesized at a greater rate than alpha mRNA at every developmental stage. In contrast to the excess accumulation of beta mRNA in spleen cells, synthesis of alpha- and beta-globin chains remains balanced throughout erythroid development. These data suggest that during erythropoiesis in this system, equal synthesis of alpha and beta globin involves regulation at both transcriptional and post-transcriptional levels.
Amino-acid sequence of tropomyosin-binding component of rabbit skeletal muscle troponin.
Authors: Pearlstone J R , Carpenter M R , Johnson P , Smillie L B
Published: May 2006

The complete amino-acid sequence of rabbit skeletal troponin-T is reported. The protein consists of a single polypeptide chain of 259 amino acids; it has an acetylated amino terminus and a molecular weight of 30,503. The sequence was determined by manual and/or automated Edman degradation techniques on the six fragments obtained after cleavage with cyanogen bromide. The larger fragments were further digested with trypsin, chymotrypsin, alpha-lytic protease, thermolysin, or pepsin to obtain smaller fragments suitable for manual sequencing. About 50% of the residues are charged at neutral pH with highly acidic amino-terminal (residues 1-39) and highly basic carboxyl-terminal regions (residues 221-259). Predictions of secondary structure indicate 37% helical content with two long sections (residues 80-102 and 122-146) in that portion of the molecule implicated in binding to tropomyocin. Two of the three phosphorylated sites in the molecule are located at serine-1 and serine-149 or -150. The sequence about the latter site resembles somewhat the phosphorylase kinase phosphorylation sites in phosphorylase alpha and troponin-I.
A chromosomal gene required for killer plasmid expression, mating, and spore maturation in Saccharomyces cerevisiae.
Authors: Leibowitz M J , Wickner R B
Published: May 2006

"Killer" strains of Saccharomyces cerevisiae are those that harbor a double-stranded RNA plasmid and secrete a toxin that kills only strains not carrying this plasmid (sensitives). Two chromosomal genes (kex1 and kex2) are required for the secretion of toxin by plasmid-carrying strains. The kex2 gene, which maps at a site distinct from the mating-type locus, is also required for normal mating by alpha strains and meiotic sporulation in all strains. Strains that are alpha mating-type and kex2 fail to secrete the pheromone alpha-factor or to respond to the alpha-factor II pheromone which causes a morphological change, but they do respond to alpha-factor I which causes G1 arrest in alpha cells. Strains that are alpha mating-type and kex2 show no defect in mating; pheromone secretion, or response to alpha-factor. Diploids that are homozygous for the kex2 mutation, unlike wildtype or heterozygous diploids, fail to undergo sporulation, with the defect occurring in the final spore maturation stage. These same defects in the sexual cycle are present in all kex2 mutants independent of the presence of the "killer" plasmid.
Antibodies as a means of isolating and characterizing biologically active substances: presence of a non-peptide, morphine-like compound in the central nervous system.
Authors: Gintzler A R , Levy A , Spector S
Published: May 2006

Antibodies generated against small molecular weight substances such as drugs are being used to isolate and characterize biologically active agonists. A morphine-like compound can be extracted from brain of various species which has determinant groups that are recognized by specific morphine antibodies. It has a regional distribution which can be quantitated as immuno-equivalents. Immunological, chemical and chromatographic tests show great similatiries of the compound to morphine. This morphine-like compound has biological activity as it inhibits the electrically induced contractions both of the guinea pig ileum and mouse vas deferens but the inhibition is not reversed by naloxone or naltrexone.
Redox titration of fluorescence yield of photosystem II
Authors: Ke Bacon , Hawkridge Fred. M. , Sahu Saura
Published: May 2006

The variable fluorescence yield of photosystem II is dependent on the redox state of the fluorescence quencher molecule or the primary electron acceptor of the system. We have carried out redox titrations of fluorescence yield of a photochemically active photosystem-II reaction-center particle and have measured the redox potential of the photosystem-II primary acceptor.

During reductive titrations using dithionite as the reductant, only a single quenching transition was observed. For instance, at pH 7.0, the midpoint potential of the fluorescence transition is -325 mV, and those at a pH between 6.0 and 7.5 are consistent with a pH dependence of about 60 mV/pH unit. At a given pH, the midpoint potential of the transition closely corresponds to that of the most negative transition previously measured in unfractionated chloroplasts (both by chemical reductive titration). Oxidative titrations using ferricyanide as the oxidant yielded hysteresis in the titration curves.

Similar changes in fluorescence yield were observed in redox titrations by electrochemical reduction or oxidation. Electrochemical reductive and oxidative titrations yielded reversible transitions, contrary to the hysteresis observed during chemical oxidative titration. From coulometric-titration data, we have estimated that most likely one electron is involved in the redox transition of the fluorescence-quencher or primary-electron-acceptor molecule of photosystem II. These findings are consistent with the current proposal that a membrane-bound plastoquinone functions as the primary acceptor of photosystem II.
Mutagenicity of aflatoxins related to their metabolism and carcinogenic potential.
Authors: Wong J J , Hsieh D P
Published: May 2006

Aflatoxins and their animal biotransformation products were screened for carcinogenic potential using the Ames' in vitro microbial detection system for carcinogens as bacterial mutagens [B. N. Ames et al. (1973) Proc. Natl. Acad. Sci. USA 70,2281-2285]. Aflatoxicol, aflatoxins G1 and M1, aflatoxicol H1, and aflatoxins Q1, B2, P1, G2, B2a, and G2a, listed in order of decreasing mutagenic potency, were all less active than aflatoxin B1. No compound possesses activity in the absence of the rat liver preparation, and this indicates none of the animal metabolites are the ultimate mutagenic and/or carcinogenic species. The relative mutagenic potency observed with this in vitro system qualitatively correlates with in vivo carcinogenic data. Comparison of both methods indicates: (i) aflatoxin B1 possessed the structure optimal for both mutagenicity and carcinogenicity, (ii) the decreased carcinogenicity of various animal metabolites is associated with their decreased mutagenicity, and (iii) the 2,3-double bond is involved in both the mutagenic and carcinogenic activity of aflatoxins. The Ames' assay has been demonstrated to be an extremely promising (toxicological) tool for the analysis of mycotoxins for mutagenic and/or carcinogenic activity.
Deposition of histone onto the replicating chromosome: newly synthesized histone is not found near the replication fork.
Authors: Jackson V , Granner D , Chalkley R
Published: May 2006

We have studied the site of deposition of newly synthesized histone. It appears to be randomly distributed over the chromosomal material and does not become associated specifically with immediately post-replicational DNA, nor is it deposited in discrete continuous regions distal to the sites of DNA synthesis. The newly synthesized DNA, however, rapidly acquires a complement of chromosomal proteins; presumably, preexisting histones must migrate to become associated with post-replicational DNA.
Tetrodotoxin-resistant dendritic spikes in avian Purkinje cells.
Authors: Llinás R , Hess R
Published: May 2006

Electrophysiological evidence for the existence of dendritic spikes in the Purkinje cells of pigeon cerebellar cortex is presented. Intradendritic records indicate that the electroresponsive properties of the dendrites linger after voltage-dependent sodium and potassium conductances are reduced by superfusion of the cortex with Ringer's solution containing 20 mug/ml tetrodotoxin and 5 mM 3-aminopyridine. Dendritic spikes could be evoked, in the complete absence of activity from all cerebellar afferents and from the soma and axon of the Purkinje cells, by direct electrical activation of the surface of the cerebellar cortex or by intracellular injection of current via the recording electrode. The denritic electroresponsiveness was blocked by superfusion with 20 mM Mn2+ or Co2+. It is thus concluded that dendrites of Purkinje cells in birds are capable of generating calcium-dependent spikes. The possible role of such a calcium current in neuronal function is discussed.
Implications of cross inhibitory interactions of potential mediators of hormone and neurotransmitter action.
Authors: Van Cauter E , Hardman J G , Dumont J E
Published: May 2006

Mediators of hormone and neurotransmitter action may exert negative control on the accumulation of one another (adenosine 3':5'-cyclic monophosphate, or conversely). A model in which one agonist stimulates the formation of two mediators which inhibit each other's accumulation has been simulated. Three types of agonist-receptor interaction, five mechanisms of inhibition, and three types of basal activity have been considered which lead to a set of 45 descriptions of the general cross inhibition model. For these submodels, pattern of the relation of agonist to mediator concentrations at steady state conditions have been defined. Some patterns are complex with mediator curves exhibiting extrema, one a maximum and the other a minimum. The complexity of the pattern depends on the submodel and on the degree of asymmetry between the parameters of each of the mediator pathways (e.g.,affinities for the agonist, strength of the inhibitions, etc.). This simple model can thus account for complex experimental results without requiring the postulation of elaborate molecular models of agonist-receptor interaction. The simulations presented emphasize the necessity of investigating a wide range of agonist concentrations.
Supersaturation in sickle cell hemoglobin solutions.
Authors: Hofrichter J , Ross P D , Eaton W A
Published: May 2006

The kinetic inhibition of the gelation of hemoglobin S is compared to the change in hemoglobin S soulbility, when the solubility is altered by carbon monoxide, pH, or urea. By means of a new technique, the delay time and the extent of gelation are measured on the same sample. They delay time, td, is found to be proportional to a high power (30-40) of the hemoglobin S solubility. Togehter with the previously reported concentration dependence, this result demonstrates that the rate is proportional to a high power of the supersaturation, S, defined as the ratio of the total hemoglobin S concentration to the equilibrium solubility. The results obey the supersaturation equation td-1 = gammaSn, where gamma is an empirical constant (about 10(-7) sec-1) and n is about 35. The supersaturation equation can successfully account for observations on the kinetics of cell sickling and is therefore used to estimate the increase in the delay time for sickling necessary to produce significant clinical benefit to patients with sickle cell disease.
Restoration of oxidative phosphorylation by purified N,N'-dicyclohexylcarbodiimide-sensitive latent adenosinetriphosphatase from Mycobacterium phlei.
Authors: Lee S H , Cohen N S , Brodie A F
Published: May 2006

The N,N'-dicyclohexylcarbodiimide (DCCD)-sensitive latent adenosinetriphosphatase (ATPase) (EC 3.6.1.3; ATP phosphohydrolase) from Mycobacterium phlei has been purified to homogeneity and used to resotre oxidative phosphorylation to detergent-extracted membranes. The phosphorylation was inhibited by DCCD any by tetraphenylboron and valinomycin. The enzyme was solubilized from the membrane vesicles by treatment with cholate followed by extraction with Triton X-100. After partial purification on a sucrose gradient, the enzyme was purified to homogeneity by affinity chromatography on Sepharose coupled to ADP. The DCCD-sensitive latent ATPase of coupling factor from M. phlei consists of two components, the latent ATPase (Bcf4), which is insensitive to DCCD, and an intrinsic membrane component, BCF0. This hydrophobic portion of the DCCD-sensitive ATPase was partially purified on a sucrose gradient after solubilization with detergents from membrane vesicles that had been first depleted of the BCF4 by washing with 0.25 M sucrose. When BCF0 was combined with purified BCF4, the latent ATPase of the resulting complex was sensitive to DCCD. Moreover, like the purified DCCD-sensitive latent ATPase, the combined BCF4 and BCF0 restored coupled phosphorylation to detergent-extracted membranes.
Preparative fractionation of DNA restriction fragments by reversed phase column chromatography.
Authors: Hardies S C , Wells R D
Published: May 2006

Reversed phase column chromatography on RPC-5 resin was used to fractionate milligram quantities of DNA fragments generated by restriction endonucleases. Fractionation was on the basis of size, the presence or absence of sticky ends, and at least one as yet undertermined property.
Inhibition of erythrocyte sickling by cystamine, a thiol reagent.
Authors: Hassan W , Beuzard Y , Rosa J
Published: May 2006

Incubation of sickle cells with cystamine, a thiol reagnet, resulted in the formation of an intracellular S-ethylamine derivative. The rate of the reaction was dependent upon the cystamine concentration, the temperature, and the duration of the incubation. The cystamine-treated cells demonstrated a marked inhibition of sickling under hypoxic conditions, a decrease in their mean corpuscular hemoglobin concentration, and a significant increase in their oxygen affinity. The oxygen affinity of these cells was less dependent on their mean corpuscular hemoglobin concentration than that of untreated sickle cells. The minimum gelling concentration of S-ethylamine doxyhemoglobin S was slightly increased. Cystamine did not affect the intracellular pH nor the 2,3-diphosphoglycerate level. The exact contribution of the interrelated factors in cystamine inhibition of sickling (changes in oxygen affinity, mean corpuscular hemoglobin concentration, and minimum gelling concentration) has yet to be determined.
Suppression of lytic effect of beta lactams on Escherichia coli and other bacteria.
Authors: Goodell E W , Lopez R , Tomasz A
Published: May 2006

Growth of E. coli at pH 5 protected the bacteria against the lytic effect of beta lactam antibiotics typically observed when the cells are grown at pH 7 or 7.5, i.e., the pH values routinely used in laboratory experiments. In contrast, the typical effects of beta lactam antibiotics on cellular shape and elongation and cell division appeared to be similar in cultures grown under neutral and acid pH conditions. The pH-dependent antibiotic tolerance can also be demonstrated with pneumococci, staphylococci, streptococci, and Bacillus subtilis. We suggest that the mechanism of the pH-dependent antibiotic tolerance may involve either the production of a more stable plasma membrane or the suppression of the activity of a murein hydrolase(s) that catalyzes the antibiotic-induced lysis; at least a fraction of these enzyme molecules may be localized at the cell surface and be accessible to experimental manipulation.
Morphinomimetic activity of synthetic fragments of beta-lipotropin and analogs.
Authors: Ling N , Guillemin R
Published: May 2006

In the myenteric plexus-longitudinal muscle bioassay, beta-endorphin, i.e., beta-lipotropin (beta-LPH)-[61-91], has a potency of 450 with confidence limits of 281-966 when Met5-enkephalin is used as a reference standard with a potency of 100. The primary amide and the ethylamide of Met5-enkephalin have potencies statistically overlapping with that of beta-endorphin. The primary amide of alpha-endorphin has twice the potency of the free acid form of alpha-endorphin. An intact NH2-terminal tyrosine is not necessary for full intrinsic activity. The shortest fragment of beta-LPH with morphinomimetic activity is beta-LPH-[61-64].
A mechanism of duplex DNA replication revealed by enzymatic studies of phage phi X174: catalytic strand separation in advance of replication.
Authors: Scott J F , Eisenberg S , Bertsch L L , Kornberg A
Published: May 2006

The enzyme system for duplicating the duplex, circular DNA of phage phi X174 (replicative form) in stage II of the replicative life cycle was shown to proceed in two steps: synthesis of the viral (+) strand ]stage II(+)], followed by synthesis of the complementary (-) strand ]stage II(-)] [Eisenberg et al. (1976) Proc. Natl. Acad. Sci. USA 73, 3151-3155]. Novel features of the mechanism of the stage II(+) reaction have now been observed. The product, synthesized in extensive net quantities, is a covalently closed, circular, single-stranded DNA. The supercoiled replicative form I template and three of the four required proteins--the phage-induced cistron A protein (cis A), the host rep protein (rep), and the DNA polymerase III holoenzyme (holoenzyme)--act catalytically; the Escherichia coli DNA unwinding (or binding) protein binds the product stoichiometrically. In a reaction uncoupled from replication, cis A, rep, DNA binding protein, ATP, and Mg2+ separate the supercoiled replicative form I into its component single strands coated with DNA binding protein. In the presence of Mg2+, cis A, nicks the replicative form I; rep, ATP, and Mg2+ achieve strand separation with a concurrent cleavage of ATP and binding of DNA binding protein to the single strands. rep exhibits a single-stranded DNA-dependent ATPase activity. These observations suggest that the rep enzymatically melts the duplex at the replicating fork, using energy provided by ATP; this mechanism may apply to the replication of the E. coli chromosome as well.
A protein covalently linked to poliovirus genome RNA.
Authors: Lee Y F , Nomoto A , Detjen B M , Wimmer E
Published: May 2006

Poliovirion [32P]RNA, after digestion with RNase T2, yields mononucleotides and a labeled compound "X," which is not negatively charged at pH 5. X contains, relative to the label in virion RNA, one to two phosphates and is partially acid insoluble. It can be labeled with tritiated amino acids 3 hr after infection, is insoluble in chloroform/methanol, and can be digested with Pronase. These observations suggest that X is a protein. The protein cannot be removed from the polio genome when the RNA is (i) sedimented through a sucrose gradient in 0.5 M NaCl, (ii) heated to 100 degrees in the presence of sodium dodecyl sulfate followed by sedimentation through a sucrose gradient in 80% dimethylsulfoxide, or (iii) banded in 4 M cesium trichloroacetate. Digestion of the 32P-labeled protein with Pronase yields one major 32P-labeled product, which contains pUp. The protein migrates faster than capsid protein VP4 in a polyacrylamide gel. Our data show that the genome of poliovirus, but not poliovirus mRNA [A. Nomoto, Y. F. Lee, and E. Wimmer (1976) Proc. Natl. Acad. Sci. USA 73, 375-380], is covalently attached to a small virus-coded protein (molecular weight less than 7000), which we call VPg. VPg is probably linked to the 5' end of the polio genome. Possible functions of VPg in viral replication are discussed.
Ionophores stimulate prostaglandin and thromboxane biosynthesis
Authors: Knapp Howard R. , Oelz Oswald , Roberts L. Jackson , Sweetman Brian J. , Oates John A. , Reed Peter W.
Published: May 2006

The role of calcium in triggering prostaglandin and thromboxane synthesis was studied in several systems with ionophores of different ion specificities. Divalent cationophore A23187 stimulates prostaglandin and thromboxane production by washed human platelets in a concentration-dependent manner (0.3-9 μM). A23187 also induces an antimycin A-insensitive burst in oxygen utilization which is partially blocked by 5 mM aspirin or 10 μM indomethacin. Under our conditions, A23187 (up to 10 μM) does not appear to damage platelet membranes since it does not cause appreciable loss of lactate dehydrogenase or β-glucuronidase. Mono- and divalent cationophore X537A also stimulates platelet thromboxane B
2
production and oxygen utilization, but monovalent cationophores nigericin, monensin A, A204, and valinomycin have no effect. The synthesis of prostaglandins E
2
, D
2
, and F
2α
by rat renal medulla mince is stimulated by 1 and 5 μM A23187 without changes in tissue ATP content, lactate output, or K
+
efflux. X537A, monensin A, and nigericin (all 5 μM) stimulate both prostaglandin output and K
+
efflux from renal medulla, while 5 μM valinomycin or A204 has no effect on either. None of the ionophores stimulates renomedullary prostaglandin production if calcium is omitted from the incubation medium. A23187 also stimulates prostaglandin production by human lymphoma cells, rat stomach and trachea preparations, and guinea pig polymorphonuclear leukocytes. These observations suggest a major role for Ca
2+
in stimulating prostaglandin and thromboxane biosynthesis, and also indicate that prostaglandin and/or thromboxane release may partially mediate some of the previously described effects of ionophores on cells and tissues.