bluuebunny/crossref_metadata_2025 huggingface dataset:
Direct identification of the calcium-binding amino acid, gamma-carboxyglutamate, in mineralized tissue.
Authors: Hauschka P V , Lian J B , Gallop P M
Published: May 2006

A direct approach has been developed for quantitative identification of the calcium-binding amino acid, gamma-carboxyglutamate, in proteins. This should be advantageous for the study of numerous systems where specific roles for the binding of calcium or other divalent cations are suspected. Investigation of mineralized tissue, where calcium-binding proteins are implicated in the mineralization process, revealed that gamma-carboxyglutamate was present in proteins solubilized from chicken bone with neutral aqueous ethylenediamine tetraacetic acid. This was established by direct isolation of the amino acid from alkaline hydrolysates and its quantitative conversion to glutamic acid by decarboxylation in 0.05 M HCl at 100 degrees. The kinetics of decarboxylation and chromatographic behavior are identical to those of gamma-carboxyglutamate from human prothrombin. After resolution of the soluble bone proteins by phosphate gradient elution from hydroxyapatite, gamma-carboxyglutamate was found to be concentrated primarily in one BaSO4-adsorbable anionic protein species; bone collagen was devoid of the amino acid. In view of the recently discovered requirement of vitamin K for generation of calcium binding sites (gamma-carboxyglutamate) by gamma-carboxylation of specific glutamic acid residues in prothrombin, our findings may implicate vitamin K metabolism in normal bone development and suggest a role for the gamma-carboxyglutamate-rich protein in regulation of calcium salt deposition in mineralized tissues.
Polypeptide chain initiation in eukaryotes: initiation factor MP in Artemia salina embryos.
Authors: Filipowicz W , Sierra J M , Ochoa S
Published: May 2006

The activity of IF-MP, a polypeptide chain initiation factor that forms a ternary complex with eukaryotic initiator Met-tRNA and GTP and promotes binding of the initiator to 40S ribosomes, is very low in undeveloped Artemia salina embryos but increases over 20-fold following resumption of development upon hydration of the cysts. The factor is present in both the ribosomal salt wash and high-speed-supernatant. Its specific activity is 50 times higher in the wash but its total activity is only about twice as high in the wash as in the supernatant. As is true of IF-MP from other eukaryotic sources, the A. salina factor is specific for eukaryotic Met-tRNAi and sensitive to SH-reagents, and its activity is GTP dependent.
Ubiquinone-mediated coupling of NADH dehydrogenase to active transport in membrane vesicles from Escherichia coli.
Authors: Stroobant P , Kaback H R
Published: May 2006

Addition of ubiquinone-1 to E. coli ML 308-225 membrane vesicles dramatically increases coupling between NADH oxidation and active transport such that initial rates and steady-state levels of lactose and amino-acid accumulation are comparable to those observed during D-lactate oxidation. Similar but less dramatic effects are observed with the quinone and succinate or L-lactate. In the presence of NADH and ubiquinone-1, the vesicles also generate a membrane potential (interior negative) that is similar in magnitude to that observed in the presence of D-lactate. Stimulation of NADH-dependent transport by ubiquinone-1 cannot be accounted for by increased rates of oxidation of NADH, and the effect of the quinone on NADH-dependent lactose transport is not observed in vesicles depleted of NADH dehydrogenase activity. Thus, it is apparent that ubiquinone-1 shunts electrons from NADH dehydrogenase [NADH:(acceptor)oxidoreductase; EC 1.6.99.3] to the portion of the respiratory chain containing the energy-coupling site. The findings demonstrate unequivocally that inefficient coupling of NADH oxidation to active transport cannot be due to the presence of inverted vesicles. In addition, they provide further support for specific localization of the energy-coupling site.
Biosynthesis of mouse interferon by translation of its messenger RNA in a cell-free system.
Authors: Thang M N , Thang D C , De Maeyer E , Montagnier L
Published: May 2006

A fraction of mouse RNA containing messenger RNA coding for mouse interferon was translated with high efficiency in a wheat germ system into a fully active product. This product fulfills the criteria for mouse interferon, namely: (1) it was active against vesicular stomatitis virus and herpes simplex virus in mouse cells; (2) its antiviral activity was species specific; (3) its activity was completely neutralized by mouse anti-interferon serum. The synthesis of interferon in this cell-free system requires the presence of spermine.
Immunochemical evidence for a common variable region in three immunoglobulin classes in the same individual.
Authors: Grubb A O , Zettervall O H
Published: May 2006

One IgG1(kappa), one IgM(kappa), and one IgA1(kappa) monoclonal (M)-component were purified from one human serum. Rabbit antisera were raised against the IgG and IgM M-components and were absorbed until specific for idiotypic determinants on these molecules. All three M-components gave reactions of immunological identity when tested by double radial immunodiffusion with either of the two idiotype-specific antisera. Both heavy and light chains were isolated from each of the three M-components and all preparations inhibited formation of idiotypic precipitates. None of these preparations formed precipitates with idiotype-specific antisera alone. When heavy or light chains of one M-component were hybridized with light or heavy chains from the other M-components the resultant molecules precipitated with anti-idiotypic serum. Hybrids with chains from polyclonal IgG were not precipitable with such antiserum. These results indicate that the variable region of the heavy chains of these M-components of three different immunoglobulin classes are closely similar, if not identical.
Body weight and food intake at early estrus of rats on a high-fat diet.
Authors: Frisch R E , Hegsted D M , Yoshinaga K
Published: May 2006

Body weight, food intake, and age at vaginal opening and estrus were studied for two groups of weanling rats (age 21 days), fed on high-fat (24.6% by weight) and low-fat (5.0%) diets. Fat was substituted isocalorically for carbohydrate in the high-fat diet. The high-fat rats had estrus at 33.3 +/- 0.8 days, significantly earlier (P less than 0.001) than the age at estrus, 37.4 +/- 0.7 days, of the low-fat rats. Estrus was simultaneous with vaginal opening in 81% of the high-fat rats, in comparison to 48% of the low-fat rats. The caloric intake per 100 g of body weight of the high-fat and low-fat rats did not differ at vaginal opening or at estrus, whereas the two groups differed significantly at both events in age, body weight, absolute food intake (g/day), and relative food intake (g/100 g of body weight per day) and absolute caloric intake (calories/day). Caloric intake/100 g of body weight as a function of chronological age first increased and then decreased steadily before estrus for both high-fat and low-fat rats. The findings support Kennedy's hypothesis that a food intake signal, now further defined as caloric intake/100 g of body weight, is a signal for puberty, and are in accord with the hypothesis that a critical body composition of fatness is essential for estrus in the rat, as in the human female.
Effect of hypothalamic deafferentation on thyrotropin-releasing hormone levels in rat brain.
Authors: Brownstein M J , Utiger R D , Palkovits M , Kizer J S
Published: May 2006

The medial basal hypothalamus was isolated from the remainder of the brain of the rat using a Halász knife. Ten to 14 days after the surgical procedure the concentration of thyrotropin-releasing hormone within the island of hypothalamic tissue was 76% lower than in tissue from sham-operated control rats. Thus, much of the thyrotropin-releasing hormone that is normally present in the medial basal hypothalamus may be synthesized by cells outside of this region. There were no reductions in hormone levels in regions outside of the hypothalamic island after the surgical procedure. Extrahypothalamic thyrotropin-releasing hormone does not appear to be produced by hypothalamic neurosecretory cells.
Effects of estrogen on gene expression in chick oviduct: nuclear receptor levels and initiation of transcription.
Authors: Tsai S Y , Tsai M J , Schwartz R , Kalimi M , Clark J H , O'Malley B W
Published: May 2006

Estrogen (diethylstilbesterol) was administered in vivo to chicks for various time periods. Chromatin was then prepared from oviduct nuclei and assayed for its capacity to support initiation of RNA chain synthesis in vitro in the presence of saturating levels of Escherichia coli RNA polymerase (RNA nucleotidyltransferase; nucleosidetriphosphate:RNA nucleotidyltransferase; EC 2.7.7.6). These same nuclei were also assayed by a [3H]estradiol exchange assay for their endogenous receptor content. The number of available initiation sites for RNA synthesis on chromatin was shown to correlate with the endogenous levels of nuclear estrogen receptor. A decrease in the nuclear concentration of estrogen receptor molecules and the concentration of initiation sites for RNA synthesis occurred during withdrawal of estrogen from previously stimulated chicks. Both parameters declined with a similar half-life. When estrogen was readministered to withdrawn chicks, the number of initiation sites increased 2-fold as early as 30 min and approached a maximal level (3-fold) by 1 hr. During the same period of restimulation with estrogen, the number of estrogen receptor molecules bound to nuclei increased to a maximum at 20 min and then declined at 1 hr to a steady-state level 2-fold higher than the withdrawn chicks. Simultaneous measurements of RNA chain length and RNA chain propagation rate demonstrated that parameters remained relatively constant throughout estrogen withdrawal as well as secondary stimulation. The temporal correlation between changes in the levels of nuclear-bound estrogen receptor and the number of RNA chain initiation sites on chromatin prepared from these same nuclei strongly suggested that the hormone receptor complexes act on chromatin to mediate these changes in genetic transcriptional activity.
Mechanism of dissociation of ribosomes of Escherichia coli by initiation factor IF-3.
Authors: Gottleib M , Davis B D , Thompson R C
Published: May 2006

Initiation factor IF-3 clearly can cause dissociation of ribosomes by binding to 30S subunits and thus shifting the spontaneous equilibrium, but it theoretically may also do so by binding to 70S ribosomes. Previously reported experiments with differentially labeled ribosomes and subunits seemed to eliminate the latter mechanism, but these experiments neglected a substantial decrease in the specific activity of the added subunits resulting from net dissociation of the ribosomes by IF-3. The present experiments eliminate or correct this effect. The results exclude direct action on 70S ribosomes as a significant mechanism of dissociation by IF-3.
Effect of extradiol-17beta on the synthesis of specific uterine nonhistone chromosomal proteins.
Authors: Cohen M E , Hamilton T H
Published: May 2006

The synthesis of specific nonhistone chromosomal proteins in the uterus of the ovariectomized rat was examined as a function of time after treatment with estradiol-17beta. Sequential stimulations in the rates of synthesis of at least five nonhistone chromosomal proteins having molecular weights of 96,000, 70,500, 29,400, 20,700, and 16,400, respectively, were observed. The rate of synthesis of the nonhistone chromosomal protein having a molecular weight of 70,500 was increased at 1 hr after hormone treatment. This was the first nonhistone chromosomal protein to be induced by estrogen, and its induction was blocked by pretreatment with actinomycin D. The data reported suggest but do not prove that this protein is the 4.5 S estrogen receptor, and that it is the induced nuclear acidic protein described earlier by Teng and Hamilton. The rates of synthesis of the nonhistone proteins with molecular weights of 96,000, 29,400, 20,700, and 16,400 were increased at 3,5,24, and 24 hr, respectively, after hormone treatment.
Role of carnitine in hepatic ketogenesis.
Authors: McGarry J D , Robles-Valdes C , Foster D W
Published: May 2006

The enhancement of long-chain fatty acid oxidation and ketogenesis in the perfused rat liver, whether induced acutely by treatment of fed animals with anti-insulin serum or glucagon, or over the longer term by starvation or the induction of alloxan diabetes, was found to ba accompanied by a proportional elevation in the tissue carnitine content. Moreover, when added to the medium perfusing livers from fed rats, carnitine stimulated ketogenesis from oleic acid. The findings suggest that the increased fatty acid flux through the carnitine acyltransferase (carnitine palmitoyl-transferase; palmitoyl-CoA:L-carnitine O-palmitoyltransferase; EC 2.3.1.21) reaction brought about by glucagon excess, with or without insulin deficiency, is mediated, at least in part, by elevation in the liver carnitine concentration.
Rous sarcoma virus activates embryonic globin genes in chicken fibroblasts.
Authors: Groudine M , Weintraub H
Published: May 2006

Complementary DNA (cDNA) specific for chick globin mRNA sequences fails to hybridize to total RNA extracted from chicken fibroblasts. After infection by Rous sarcoma virus, RNA complementary to globin cDNA is detectable in 100-500 copies per cell. Infection of fibroblasts with the transformation defective (td) deletion mutant of Rous sarcoma virus leads to normal virus production, but not to host cell transformation or accumulation of RNA sequences complementary to globin cDNA. Our evidence shows that the globin genes activated by Rous sarcoma virus are those specified by embryonic chick red cells; adult-specific globin sequences were not detected.
Structure of tight junctions in epithelia with different permeability.
Authors: Martínez-Palomo A , Erlij D
Published: May 2006

Freeze-fracture studies have shown a network of intramembrane fibrils in the tight junctions of epithelia. A direct correlation between the number of fibrils and junctional permeability has been suggested by previous studies. However, we have made two groups of observations showing that junctional permeability is not univocally related to the complexity of the network revealed by freeze-fracture. (i) The tight junctions of the rabbit ileum mucosa are permeable to lanthanum, although they have a complex network of fibrils resembling the junctions of toad urinary bladder, which are impermeable to lanthanum. (ii) The tight junctions of the toad urinary bladder are normally of low permeability; however, when the luminal solution is made hypertonic with lysine, junctional permeability markedly increases and lanthanum permeates through the tight junctions. In freeze-fracture replicas, no differences between the fibrils of control and lysine-treated bladders were found. Our results indicate that junctional permeability is controlled not only by the complexity of the fibrilar network, but that some features of the junctions or the fibrils themselves, not yet revealed by electron microscopy, play a central role in regulating epithelial permeability.
Use of gene 32 protein staining of single-strand polynucleotides for gene mapping by electron microscopy: application to the phi80d3ilvsu+7 system.
Authors: Wu M , Davidson N
Published: May 2006

A method for visualizing RNA-DNA duplex regions along a single strand of DNA in the electron microscope is described. A preparation of RNA molecules is hybridized to a long DNA strand containing the coding sequences (genes) for some of the RNAs. T4 gene 32 protein, which binds selectively and cooperatively only to the single-strand regions, is added, followed by glutaraldehyde. The resulting nucleic acid-gene 32 complex is adsorbed to the surface of an electron microscope grid in the presence of ethidium bromide. The single-strand regions are relatively thick (8.5 nm) compared to the duplex (RNA-DNA hybrid) regions (3.5 nm), so that the two kinds of regions are readily recognized by electron microscopy. In favorable cases, tRNA-DNA hybrids of length about 80 nucleotide pairs can be recognized (although with difficulty). The positions of a number of interesting genetic sequences on the DNA of the transducing phage phi80d3ilvsu+7 have been mapped. The r strand contains 16S, 23S, and 5S rRNA coding sequences in that order. The spacer between 16S and 23S genes has a length of 500 nucleotides and contains the coding sequence for a tRNA2Glu gene in agreement with previous biochemical observations. The spacer between the 23S and 5S genes has a length of 180 nucleotides. The su+7 tRNATrp coding sequence has been mapped on the l strand at a position just to the left of the ilv genes. Secondary structure loops due to short inverted repeat sequences flanking the 16S, 23S, tRNATrp, and F sequences in the DNA have been observed.
Stimulation and inhibition of anti-hapten responses in guinea pigs immunized with hybrid liposomes.
Authors: Kochibe N , Nicolotti R A , Davie J M , Kinsky S C
Published: May 2006

Guinea pigs were immunized with liposomal model membranes containing phosphatidylethanolamine (PE) or glycerophosphorylethanolamine (GPE) derivatives in which the amino function was substituted with either dinitrophenylaminocaproyl (Dnp-Cap) or mono(p-azobenzenearsonic acid)tyrosyl (ABA-Tyr) residues. Previous studies have demonstrated that hapten-specific antibodies are elicited by DNP-Cap-PE or ABA-Tyr-PE sensitized liposomes and that cell-mediated immunity is induced by ABA-Tyr-PE (but not Dnp-Cap-PE) sensitized liposomes. These liposomes differ from conventional immunogens in which haptens are covalently attached to immunogenic carriers. This investigation describes two new aspects of liposomal immunogenicity in animals immunized with hybrid liposomes containing both Dnp-Cap-PE and ABA-Tyr-PE. (1) Stimulation of the anti-Dnp response by incorporation of increasing amounts of ABA-Tyr-PE; (2) inhibition of anti-ABA antibody formation by incorporation of increasing amounts of DNnp-Cap-PE. The two phenomena are dependent on the presence of each determinant in the same lipid bilayer. Thus, entrapment of the water-soluble deacylated derivative of ABA-Tyr-PE (i.e., ABA-Tyr-GPE) in a aqueous compartments of Dnp-Cap-PE sensitized liposomes does not enhance anti-Dnp antibody production. Similarly, entrapment of the non-amphipathic derivative of DNP-Cap-PE (i.e., Dnp-Cap-GPE) within ABA-Tyr-PE sensitized liposomes does not suppress anti-ABA antibody formation. Furthermore, mixtures of Dnp-Cap-PE sensitized liposomes and ABA-Tyr-PE sensitized liposomes neither stimulated nor inhibited the anti-hapten responses. These results indicate that preparation of hybrid liposomes with different N-substituted PE derivatives provides an extremely convenient method for controlling hapten and/or immunologic carrier determinant density.
Regulation of synthesis of glutamine synthetase by adenylylated glutamine synthetase.
Authors: Foor F , Janssen K A , Magasanik B
Published: May 2006

We have examined three mutants of Klebsiella aerogenes whose genetic lesions (glnB, glnD, and glnE) are in loci unlinked to the structural gene for glutamine sythetase (glnA) and in which the control of both the level and state of adenylylation of glutamine synthetase is altered. Each mutation alters a different component of the adenylylation system of glutamine synthetase [L-glutamate:ammonia ligase (ADP-forming), EC 6.3.1.2]. Inability of the cell to deadenylylate glutamine synthetase (glnB and glnD) greatly decreases its production, while inability to adenylylate glutamine sythetase (glnE) results in its constitutively high production. These results together with our previous results indicate that adenylylated glutamine synthetase inhibits the transcription of glnA.
Cytoplasmic and nuclear binding components for 1alpha25-dihydroxyvitamin D3 in chick parathyroid glands.
Authors: Brumbaugh P F , Hughes M R , Haussler M R
Published: May 2006

Specific binding of 1 alpha,25-dihydroxyvitamin D3 [1alpha,25-(OH)2D3] to macromolecular components in the cytoplasm and nucleus is demonstrated in parathyroid glands of vitamin-D-deficient chicks. The interaction of 1alpha,25-(OH)2D3 with the cytoplasmic binding component is of high affinity (Kd = 3.2 X 10(-10) M) and high specificity [1alpha,25-(OH)2D3 greater than 25-hydroxyvitamin D3 greater than 1alpha-hydroxyvitamin D3 greater than vitamin D3 in competing with radioactive 1alpha,25-(OH)2D3]. Both cytoplasmic and nuclear hormone-macromolecular complexes sediment at 3.1 S in 0.3 M KC1-sucrose gradients, and agarose gel filtration of the components indicates an apparent molecular weight of 58,000. The 3.1S binding molecules are not observed in adrenal gland, testes, liver, or kidney, but similar receptors for 1alpha,25-(OH)2D3 have been found previously in intestine. Macromolecular species with a high affinity and preference for 25-hydroxyvitamin D3 [25-(OH)D3] are also identified in parathyroid cytosol and differ from the parathyroid 1alpha,25-(OH)2D3-binding component in that: (1) they sediment at 6 S in 0.3 M KC1-sucrose gradients, (2) they are observed in all tissues examined, (3) they have a higher affinity for 25-(OH)D3 than 1alpha,25-(OH)2d3, and (4) they are not found in the nucleus of the parathyroid glands, in vitro. The discovery of unique 1alpha,25-(OH)2D3-binding components in the parathyroid glands is consistent with the sterol hormone's action at this endocrin site and possible involvement in the regulation of parathyroid hormone synthesis and secretion.
Interferon activity produced by translation of human interferon messenger RNA in cell-free ribosomal systems and in Xenopus oöcytes.
Authors: Reynolds F H , Premkumar E , Pitha P M
Published: May 2006

Translation of messenger RNA isolated from poly(rI)-poly(rC)-induced human fibroblasts in cell-free ribosomal systems and in Xenopus oocytes resulted in the production of biologically active proteins that had the properties of human fibroblast interferon. The translation in the oocytes was much more efficient, giving approximately 500 times higher titers of interferon activity than the cell-free systems. A control messenger RNA isolated from noninduced human fibroblasts, did not code for interferon synthesis in these systems. Both messenger RNA preparations stimulated [3H]amino-acid incorporation into trichloroacetic acid-insoluble material. The radioactive products and their immunoprecipitates were electrophoresed on polyacrylamide gels under denaturing conditions. The products resulting from the translation of the control (uninduced) messenger RNA in oocytes contained a major protein of approximately 45,000 molecular weight. The messenger RNA isolated from poly(rI)-poly(rC)-induced cells stimulated the synthesis of an additional 25,000 molecular weight protein that electrophoresed in the same position as human fibroblast interferon. These results suggest that human fibroblast interferon was synthesized by the translation of its messenger RNA in Xenopus oocytes and in cell-free ribosomal systems.
Transition dipole coupling in Amide I modes of βpolypeptides
Authors: Moore W. H. , Krimm S.
Published: May 2006

Our previous introduction of transition dipole coupling helped to explain the splittings in the Amide I modes of antiparallel chain pleated sheet polyglycine I. This mechanism has now been applied to the more likely rippled sheet structure of this polypeptide as well as to the pleated sheet structure of poly(L-alanine). A satisfactorily consistent explanation of the splittings in both polypeptides is obtained. Since a previously incorporated interaction constant has not been used in the present treatment, these results show that transition dipole coupling alone can provide the physical basis for understanding these splittings. It is therefore now possible to predict with confidence the hitherto unidentified
v
(π,π) frequency of the antiparallel chain pleated sheet as well as the characteristic frequencies of the parallel chain pleated sheet.
Identification of a gene for the alpha-subunit of RNA polymerase at the str-spc region of the Escherichia coli chromosome.
Authors: Jaskunas S R , Burgess R R , Nomura M
Published: May 2006

A structural gene for the alpha-subunit of RNA polymerase (nucleosidetriphosphate:RNA nucleotidyltransferase; EC 2.7.7.6) has been identified and mapped between spcA and trkA, near 64 min on the E. coli chromosome. It appears to be coordinately expressed and possibly cotranscribed with the genes for ribosomal proteins S11, S4, and L17.
Alleopathy and spatial competition among coral reef invertebrates
Authors: Jackson J. B. C. , Buss Leo
Published: May 2006

Species of ectoprocts and solitary encrusting animals were subjected in aquaria to homogenates of 11 sympatric species of sponges and colonial ascidians. Five of the nine sponge species and one of the two ascidian species exhibited species-specific allelochemical effects. Evidence suggests that alleochemical provide a wide-spread, specific, and complex mechanism for interference competition for space among natural populations of coral reef organisms. The existence of such species-specific mechanisms may provide a basis for maintenance of diversity in space-limited systems in the absence of high levels of predation and physical disturbance.
13-C nuclear magnetic resonance studies on the mechanism of action of carbonic anhydrase.
Authors: Yeagle P L , Lochmüller C H , Henkens R W
Published: May 2006

Binding of the substrate, bicarbonate, to bovine cobalt carbonic anhydrase (carbonate hydrolyase, EC 4.2.1.1) has been studied with 13-C nuclear magnetic resonance. Two binding sites for bicarbonate have been identified. One loosely binds bicarbonate, inhibits p-nitrophenyl acetate activity, and must be the bicarbonate substrate binding site; the other tightly binds bicarbonate, is noninhibitory, and plays another role. Spinlattice relaxation times for the carbon atom of bicarbonate indicate that the substrate bicarbonate is bound directly to the metal center of the enzyme, while the other bicarbonate is bound in the outer coordination sphere of the metal. It is proposed that dehydration proceeds via HCO-3 minus coordinated directly to the metal center, while the outer sphere bicarbonate facilitates catalytically important proton transfers.
Colchicine affects kinetics of concanavalin a-mediated agglutination of hepatoma cells and plasma membranes from liver and hepatoma cells.
Authors: Nakamura J , Terayama H
Published: May 2006

Concanavalin A-mediated agglutination reactions of hepatoma cells [AH-130F(N)] and isolated liver cells, as well as of plasma membranes prepared from the liver and hepatoma, were investigated kinetically together with the effect of colchicine upon them. Concanavalin A-mediated agglutination of hepatoma cells at 25 degrees proceeded with biphasic kinetics (first and second stages of agglutination), while no appreciable agglutination of liver cells was observed in the presence of concanavalin A. The plasma membranes from the liver and hepatoma cells were similarly agglutinated with concanavalin A at 25 degrees but not at 0 degrees. The concanavalin A-mediated membrane agglutination proceeded with monophasic kinetics and was incomplete. Colchicine inhibited preferentially the second stage of concanavalin A-mediated agglutination of hepatoma cells, but it did not affect the concanavalin A-mediated agglutination of plasma membranes of both types of cells.
Testosterone stimulation of a rapidly labeled, low-molecular-weight RNA fraction in human hepatic erythroid cells in culture.
Authors: Congote L F , Solomon S
Published: May 2006

The addition of erythropoietin to cell cultures of erythroid cells of human fetal liver resulted in an increased incorporation of thymidine, adenine, and uridine into trichloroacetic acid-insoluble cell fractions and in an increased uptake of adenine and uridine into the cell. Although the effects of testosterone and erythropoietin on heme synthesis in these cells are known to be very similar, there was no effect of testosterone on the total incorporation of radioactive precursors into DNA or RNA. The RNA synthesized after short pulses of radioactive uridine, when analyzed on sucrose gradients containing 1% sodium dodecyl sulfate, consisted of a homogeneous peak sedimenting at 10 plus or minus 2 S, which is quite different from the heterogeneous, high-molecular-weight RNA synthesized under identical conditions in primary cultures of human fetal lung, kidney, or liver parenchymal cells. Addition of testosterone to liver erythroid cells in cultures for 5 hr followed by a 1-hr uridine pulse resulted in a 3-fold increase of RNA species with an average sedimentation coefficient of 14 plus or minus 3 S. The similarity with the sedimentation coefficient of the globin mRNA described in other systems and the high degree of specialization of the erythroid cells suggest that this RNA may be a stable intermediate involved in the synthesis of hemoglobin.
The structure and function of immunoglobulin domains: studies with beta-2-microglobulin on the role of the intrachain disulfide bond.
Authors: Isenman D E , Painter R H , Dorrington K J
Published: May 2006

Beta-Microglobulin, a low-molecular-weight protein structurally related to the homology regions of immunoglobulins, has been used to study the role of the intrachain disulfide bond in the unfolding of immunoglobulin domains. The intact protein could be reversibly unfolded in guanidine hydrochloride, as judged by circular dichroism and optical rotation. Similarly, reoxidation of the reduced protein, during transfer from high concentrations of guanidine to neutral aqueous buffer, yielded a product with spectral characteristics typical of the native protein. However, if the free SH groups were prevented from reoxidizing either by chemical modification or by holding them in the reduced state, the molecule appeared to be in the randomly coiled state even under conditions where the intact protein is in the native conformation, judged on the basis of chiroptical measurements. The complement-fixing activity exhibited by native beta-2-microglobulin was retained by the reduced and alkylated derivative, suggesting that the site may be formed from a linear array of amino acids. We suggest a model for the folding of beta-2-microglobulin (and immunoglobulin domains) in which one of the early folding events results in disulfide bond formation, the latter being an obligatory step for continued folding to the native state.
Contribution of the peptide backbone to the action of oxytocin analogs.
Authors: Hechter O , Kato T , Nakagawa S H , Yang F , Flouret G
Published: May 2006

This investigation was undertaken to evaluate the functional contribution of the peptide backbone of oxytocin in its interaction with receptor. Corey-Pauling-Koltun models of (Gly-7) deaminooxytocin, deaminotocinamide, and their respective retro-D-analogs built in any specific conformation (e.g., the Walter-Urry model for oxytocin) have a quai-equivalent topochemical arrangement of amino-acid side chains; however, the CO and NH elements of the peptide backbone of the retro-D-analog are reversed. The retro-D-analogs of deaminotocinamide and (Gly-7) deaminooxytocin (prepared using D-alle for L-Ile) and their respective N-formyl derivatives were assayed for uterotonic activity relative to related L-peptides. All retro-D-analogs (tested at concentrations ranging from 10-10 to 10-5 M) were devoid of angonistic (or antagonistic) activity in the isolated rat uterus, except for the retro-D-(D-alle-3, Gly-7) deaminooxytocinamine, which retains a terminal NH-2 group on the tail; the latter is a partial agonist with very low affinity. The results obtained with retro-D-analogs indicate that one or more of the elements of the peptide backbone of the tocinamide ring are essential for "occupation" and "activation" of uterine receptors. Oxytocin action may be the resultant of multiple hydrogen-bonding interactions between CO, NH, NH-2, and OH groups of the hormone with complementary groups on receptor, made possible by appropriate hydrophobic bonding.
Translation in vitro of rat brain messenger RNA coding for tubulin and actin.
Authors: Gozes I , Schmitt H , Littauer U Z
Published: May 2006

A partially purified fraction of poly(a)-rich brain mRNA coding for tubulin and actin was obtained by stepwise elution from an oligo(deoxythymidylate)-cellulose column and was efficiently translated in a wheat-germ cell-free system. The newly synthesized tubulin and actin migrated along with the authentic proteins on sodium dodecyl sulfate polyacrylamide gels and on sodium dodecyl sulfate-urea polyacrylamide gels, where tubulin alpha- and beta-subunits are separated. The two proteins synthesized in vitro were found to be biologically active; they could be induced to polymerize and were both precipitated by vinblastine. In addition, specific binding of tubulin to an affinity column of colchicine-Sepharose and actin to myosin were demonstrated.
Induction of erythroid differentiation in murine virus infected eythroleukemia cells by highly polar compounds.
Authors: Tanaka M , Levy J , Terada M , Breslow R , Rifkind R A , Marks P A
Published: May 2006

Murine-virus-infected erythroleukemia cells cultured in a medium with dimethylsulfoxide or N,N-dimethylformamide are induced to differentiate to erythroid cells. A number of highly polar compounds have a similar effect in inducing erythroid differentiation of the virus-infected cells, as assayed by the appearance of hemoglobin. These compounds are 1-methyl-1-2-piperidone, N,N-dimethylacetamide, N-methylpyrrolidinone, N-methylacetamide, 2-pyrrolidinone, propionamide, pyridine-N-oxide, piperidone, N-methylformamide, acetamide, and triethylene glycol. It has been previously reported that dimethylsulfoxide must be present during DNA synthesis and, possibly, shortly therafter, to induce differentiation. These findings are consistent with the hypothesis that dimethylsulfoxide and related polar compounds act by changing the conformation of DNA or a DNA-protein complex, causing an alteration in transcription that leads to the expression of the program of erythroid differentiation.
Immunological escape mechanism in spontaneously metastasizing mammary tumors.
Authors: Kim U , Baumler A , Carruthers C , Bielat K
Published: May 2006

Immunological and biochemical studies of spontaneously metastasizing and nonmetastasizing rat mammary carcinomas and their plasma membranes indicated that: (i) all spontaneously metastasizing tumors have little or no demonstrable glycocalyx, while all nonmetastasizing tumors have a thick glycocalyx; (ii) there is a direct relationship between the glycocalyx and immunogenicity, and an inverse relationship with the metastasizing capacity of tumor cells, properties which can be quantitated by levels of the plasma membrane marker enzyme 5'-nucleotidase (EC3.1.3.5;5'-ribonucleotide phosphohydrolase) activity; (iii) the absence of glycocalyx from the metastasizing tumor cell surface seems to result from its dissociation from plasma membranes, for solubilized cell surface antigen is readily found in the blood of metastasizing tumor bearing rats, while there was no detectable tumor cell surface antigen in the blood of the nonmetastasizing tumor hosts tested; (iv) both metastasizing and nonmetastasizing mammary tumors appear to have a common soluble cell surface antigen; (v) in addition to this common antigen, there is another membrane-bound antigen in the nonmetastasizing, immunogenic tumor cell surface which presumably is the tumor specific transplantation antigen; and (vi) this antigen is immunobiologically unique, but seems to be immunochemically related to the common soluble antigen. It is postulated that the lack of an immunogenic coat and/or the presence of solubilized tumor cell surface antigen in the blood may provide an immune escape mechanism for tumor cells by interfering with cell-mediated immune response of tumor hosts, leading to their dissemination.
Replication of colicin E1 plasmid DNA added to cell extracts.
Authors: Tomizawa J I , Sakakibara Y , Kakefuda T
Published: May 2006

Closed-circular DNA of colicin E1 plasmid can undergo a round of semiconservative replication when added to an extract of Escherichia coli. Extracts of cells that do not carry the plasmid are able to perform complete replication of the plasmid. Replication requires de novo RNA synthesis but not protein synthesis.
Abiotic, Graphitic Microstructures in Micaceous Metaquartzite about 3760 Million Years Old from Southwestern Greenland: Implications for Early Precambrian Microfossils
Authors: Nagy Bartholomew , Zumberge John E. , Nagy Lois Anne
Published: May 2006

An Early Precambrian micaceous metaquartzite subjected to low to moderate metamorphism in the Isua area of Southwestern Greenland was derived from the erosion of preexisting rocks which were probably sialic in composition. This metaquartzite may have been formed before the emergence of life. It contains globular particles of graphite arranged in narrow veins or along foliation or bedding planes. This rock contains no organic compounds besides traces of methane and no biologically significant elements associated with the graphite microstructures. Reaction of primitive methane with ferric oxides appears to have oxidized the methane to the vein graphite and reduced the ferric oxides to ferrous-ferric oxide (magnetite). The graphitic microstructures are likely to be abiotic in origin, although a biological origin is not impossible. Somewhat younger microstructures found in other locations on earth have often been described as microfossils; this origin should be reexamined on the basis of the above mentioned conclusions.
Fusion of the Escherichia coli lac genes to the ara promoter: a general technique using bacteriophage Mu-1 insertions.
Authors: Casadaban M J
Published: May 2006

The lac genes were fused to the ara promoter by means of phage phi 80 translocations of the lac and ara genes to att80. Homology for a crossover between the nonhomologous ara and lac operons was provided by mu insertions. Selection for recombinants within the mu insertions generated strains that had the ara promoter on one side of a mu insertion and the lac genes on the other side. ara-lac fusions were obtained from these strains by deleting the mu insertion. These fusions extend the techniques available for studies on the lac operon to studies on the ara operon. It should be possible to fuse other operons by this method.
Sequence of 71 nucleotides at the 3'-end of tobacco mosaic virus RNA.
Authors: Guilley H , Jonard G , Hirth L
Published: May 2006

The sequence of the first 71 nucleotides from the 3'-OH end of tobacco mosaic virus RNA has been determined. After total T1 ribonuclease digestion of the viral RNA, the oligonucleotide C-C-C-A-OH, which originates from the 3'-OH terminus of the RNA, may be readily detected by electrophoresis at pH 2.5 or pH 3.0; it is the only oligonucleotide that migrates toward the cathode at these pHs. This property has been used to screen the purified products of partial T1 ribonuclease digestion of tobacco mosaic virus RNA for the fragment originating from the 3'-end of the native molecule. The sequence of nucleotides in the 3'-terminal fragment, identified in this manner, was determined by radiochemical methods. The fragment contained 71 nucleotides; no abnormal bases could be detected. Although it has been reported that the 3'-end of tobacco mosaic virus RNA is a substrate for aminoacylation by the histidyl-tRNA synthetase of yeast or Escherichia coli, we were unable to fold the sequence into the cloverleaf structure characteristic of tRNAs.
Binding of ATP to the progesterone receptor.
Authors: Moudgil V K , Toft D O
Published: May 2006

The possible interaction of progesterone--receptor complexes with nucleotides was tested by affinity chromatography. The cytosol progesterone receptor from hen oviduct was partially purified by ammonium sulfate precipitation before use. When progesterone was bound to the receptor, the resulting complex could be selectively adsorbed onto columns of ATP-Sepharose. This interaction was reversible and of an ionic nature since it could be disrupted by high-salt conditions. A competitive binding assay was used to test the specificity of receptor binding to several other nucleotides, including ADP, AMP, and cAMP. A clear specificity for binding ATP was evident from these studies. When ATP was added to receptor preparations, the nucleotide did not affect the sedimentation properties or hormone binding characteristics of the receptor. Although the function of ATP remains unknown, these studies indicate a role of this nucleotide in some aspect of hormone receptor activity.
Cell-surface-associated nucleic acid in tumorigenic cells made visible with platinum-pyrimidine complexes by electron microscopy.
Authors: Aggarwal S K , Wagner R W , McAllister P K , Rosenberg B
Published: May 2006

Platinum-pyrimidine complexes have been used as the sole electron-dense stains for electron microscopy on 18 types of mammalian cells. These recently discovered complexes react avidly with nucleic acids in vitro, are antitumor agents, and are highly soluble in water. In cells, they are selective for regions rich in nucleic acid and make visible the cellular chromatin, nucleolus, and ribosomes. In addition, cells that are tumorigenic exhibit electron-dense patches at the plasma membrane; normal cells do not. The results of treatment of ascites sarcoma-180 cells with concanavalin A, nucleases, glycosidases, or a protease suggest that the electron-dense patches are DNA, with neuroaminic acid involved in the surface binding.
Conformation of high-molecular-weight poly(L-valine) in solid state.
Authors: Yamashita S , Yamashita T
Published: May 2006

Poly(L-valine) in various degrees of polymerization was prepared from the N-carboxyanhydride of L-valine. The high-molecular-weight polymer was fibrous and capable of forming an oriented film when cast from trifluoroacetic acid solution. The comformations were examined by Raman spectroscopy. The Raman and infrared spectra of high-molecular-weight polymer were quite different from those of low-molecular-weight and tri-fluoroacetic-acid-treated high-molecular-weight polymers. The spectral data in the amide A, I, II, III, and V regions indicated that high-molecular-weight poly(L-valine) is possibly in the alpha-helical conformation, while low-molecular-weight poly(L-valine) and high--molecular-weight poly(L-valine) treated with trifluoroacetic acid are in the beta-conformation.
Coordinated motor output in the hindlimb of the 7-day chick embryo.
Authors: Bekoff A , Stein P S , Hamburger V
Published: May 2006

Electromyographic recordings from individual identified ankle muscles of the 7-day chick embryo (stage 31) were used to determine the organization of motor output at a developmental stage shortly after the onset of spontaneous motility in the leg. During spontaneous motility of the embryo, the electromyographic recordings from the gastrocnemius, peroneus, and tibialis muscles displayed bursts of motor unit activity which alternated with periods of little or no activity. Since the control of skeletal muscle in the chick embryo is neurogenic rather than myogenic, these findings imply that the motoneurons to a given muscle are driven by a common source. Since flexor and extensor muscles are attivated at different times, different central connections to flexor and extensor motoneurons must be present in the central nerbous system of the 7-day embryo. Moreover, since inhibition is known to play an important role in the selective activation of agonist and antagonist muscles, the present results suggest that functional inhibitory synapses may be present in the lumbosacral central nervous system at this stage of development. The basic pattern of muscle activation observed in the 7-day embryo is similar to that seen in older embryos. Since these patterns appear prior to the time at which motor responses to sensory stimulation of the leg can be demonstrated, it is likely that the neural pattern generating circuits for selective activation of muscles are established in the central nervous system without reliance on functional reflexes.
Autogenous regulation of the inducible tryptophan synthase of Pseudomonas putida.
Authors: Proctor A R , Crawford I P
Published: May 2006

Mutants blocked before indole-3-glycerol phosphate formation in the tryptophan biosynthetic pathway of P. putida ("early-blocked" mutants) are unable to use indole as a source of tryptophan for growth on minimal medium. The uninduced level of tryptophan synthase [EC 4.2.1.20; L-serine hydro-lyase (adding indole)] in such mutants was thought to be responsible for this property. We have shown that levels of indole higher than those previously tested will support growth of these mutants. In addition, the growth rate of these mutants on a given indole concentration was shown to be proportional to the synthase level induced under the same conditions. This apparent induction of tryptophan synthase by indole in "early-blocked" mutants was shown to be caused by formation of the normal effector molecule, indole-3-glycerol-P, from indole. Secondary mutations occur in "early-blocked" trp strains, which enable them to grow on low concentrations of indole. One type of "indole-utilization" mutation occurs in the trpA gene, inactivating its product. Tryptophan synthase is readily induced by low concentrations of indole in these mutants, even though they are unable to convert indole to indole-3-glycerol-P. We propose that the alpha-chain of the synthase has an autogenous regulatory function, serving as the repressor or the indole-3-glycerol-P recognition component of the repressor of the trpAB operon (synthase alpha-and beta-chains). Our hypothesis holds that the trpA type of "indole-utilization" mutation alters the repressor (synthase alpha-chain) so that indole as well as indole-3-glycerol-P serves as an effector molecule for tryptophan synthase induction.
Selective blockage of initiation of host protein synthesis in RNA-virus-infected cells.
Authors: Nuss D L , Oppermann H , Koch G
Published: May 2006

Poliovirus mRNA and mRNA transcribed from vesicular stomatitis virus and reovirus genomes efficiently direct protein synthesis in vivo under experimental conditions where the initiation of host protein synthesis is selectively blocked. The selective blockage of host peptide chain initiation after exposure to hypertonic medium indicates that the translation of viral mRNA is more efficiently initiated than is the translation of host mRNA. It further suggests that virus directed suppression of host protein synthesis could proceed by a mechanism involving a nonspecific decrease in the rate of peptide chain initiation. Exposure of infected cells to hypertonic medium provides a unique tool with which to study early events in the infectious cycle by permitting the efficient unmasking of virus-specific poly-peptide synthesis.
Evolution of biosynthetic pathways: immunological approach.
Authors: Truffa-Bachi P , Guiso N , Cohen G N , Theze J , Burr B
Published: May 2006

Through the use of specific immunoadsorbent columns, it is shown that Escherichia coli aspartokinase I-homoserine dehydrogenase I, aspartokinase II-homoserine dehydrogenase II, aspartokinase III, and homoserine kinase, enzymes involved in the same complex biosynthetic pathway, share antigenic determinants. This raises the question of a common origin for the four cibtenoirart kinases. (Aspartate kinase or ATP:L aspartate 4-phosphotransferase, EC 2.7.2.4; homoserine dehydrogenase or Lhomoserine:NADP oxidoreductase, EC 1.1.1.3; homoserine kinase or ATP:L-homoserine O-phosphotransferase, EC 2.7.1.39.)