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 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

This study was an attempt to observe the effects of temperature on adsorption and one-step growth of the virus N-1 infecting the nitrogen-fixing cyanobacterium Nostoc muscorum. Adsorption rate was found to maximum at 40 degrees C whereas no adsorption occurred at 10 degrees C. The Q10 value was about 2.03 and the energy of activation, Ea was 16.3 kcal/mole for the adsorption process. The development cycle of the virus was temperature sensitive. With increase in temperature, a gradual increase in inhibition of virus yield i.e. 8.33% at 30 degrees C, 35.3% at 35 degrees C and complete inhibition at 40 degrees C was observed. Out of 7 h latent period, the early 4 h were temperature sensitive and heat treatment had a reversible inhibitory effect on virus development. The temperature treatment did not affect the rise period but burst-size was reduced.
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PMID:Effect of temperature on the adsorption and one-step growth of the Nostoc virus N-1. 41 22

1. The respiratory chain energy conservation systems of Bacillus megaterium strains D440 and M have been investigated following growth in batch and continuous culture. Respiratory membranes from these strains contained cytochromes b, aa3, o and b, c, a, o, respecitvely; both readily oxidised NADH but neither showed any pyridine nucleotide transhydrogenase activity. 2. Whole cells of both strains exhibited endogenous leads to H+/O ratios of approximately 4; when loaded with specific substrates the resultant leads to H+/O ratios indicated that proton translocating loops 1 and 2 were present in strain D440 and that loops 2 and 3 were present in strain M. 3. In situ respiratory activities were measured as a function of dilution rate during growth in continuous culture. True molar growth yields with respect to oxygen (Y02) of approximately 50 g cells-mole oxygen-1 were obtained for most of the nutrient limitations employed. Average values for YATP of 12.7 and 10.8 g cells-mole ATP equivalent-1 were subsequently calculated for strains D440 and M respectively. 4. Energy requirements for maintenance purposes were low in energy-limited cultures but were substantially increased when growth was limited by nitrogen source (NH+/4). Under the latter conditions there is probably a partial uncoupling of energy-conserving and energy-utilising processes leading to energy wastage.
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PMID:Energy conservation in Bacillus megaterium. 81 45

We have studied the effect of carbamylation on hemoglobin S (HbS) polymerization with the use of a new quantitative gelling technique. HbS gels fromed in the presence of nitrogen and dithionite (with or without carbon monoxide) at pH 7 in 0.15M phosphate were separated into sol and gel phases by centrifugation at 130,000 g. Hb concentration to the sol phase ([Hb]sol) of nonligated HbS was found to be constant (10.5 +/- 092 mM heme) over a range of original Hb concentrations from 11 to 17 mM at 24degrees C. This suggests that the HbS sol-gel equilibrium behaves as simple two-phase system. Increasing levels of total carbamylation from 0.65 to 3.65 moles CNO-/mole Hb tetramer (0.36 to 2.2 moles N-terminal/mole Hb4) progressively increases [Hb]sol. Specific activity of 14CNO-HbS was similar in the sol and gel phases, whereas COHbS appeared to be completely excluded from polymer structure of the gel. A comparison of the solubility of uncarbamylated and heavily carbamylated HbS at Co saturations ranging from 3 to 61 percent showed that the larges difference in [Hb]sol occured at the lowest ligand saturation rather than at intermediate states of ligation. Inhibition of HbS polymerization by carbamylation under these conditions, therefore, is not primarily the result of an effect on the T in equilibrium R comformational equilibrium. Our findings indicate that cyanate can interfere with HbS polymerization directly, possibly by alteration of surface binding sit(s) which are critical to aggregation. This direct action of cyanate may contribute significantly to the hematologic improvement achieved by cyanate treatment in sickle cell disease.
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PMID:Mechanism of inhibition of hemoglobin S polymerization by cyanate. 87 May 73

Three-bond 13C,H nuclear spin-spin coupling constants can be used to estimate the relative populations of the two possible tautomers of the imidazole ring in compounds containing this moiety. The mole fraction, XII, of the 1-H tautomer (i.e. the tautomer having a proton bound to the nitrogen atom at position 1 of the ring, where the ring is numbered according to IUPAC-IUB convention) can be calculated from the following equation: XII congruent to 1.705--0.164 3J(C5,H2)obs. Estimates of the predominant tautomer in L-histamine (both the neutral molecule and the monocation), and the dipeptide L-histidyl-L-glutamic acid indicate that the 1-H form is favored in basic aqueous solution. The results are compared with those obtained by other methods, and show that the present technique can provide a simple, rapid means of determining tautomeric equilibrium in imidazole derivatives.
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PMID:Application of long-range 13C,H nuclear spin-spin coupling constants in the study of imidazole tautomerism in L-histidine, and related compounds. 88 88

The purification of Methanobacterium thermoautotrophicum from a culture contaminated with a heterotrophic organism is described. A defined inorganic medium under H2/CO2 (80:20 v/v) has been developed to support growth of M. thermoautotrophicum up to a concentration of at least 1.7 g dry weight/l. In a conventional medium iron and nitrogen sources were found to be growth-limiting factors. Throughout most of the culture period the rate of transfer of hydrogen or carbon dioxide from gas to liquid was the factor which controlled the growth rate. The growth yields of bacteria were in the range of 0.6-1.6 g dry weight/mole CH4.
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PMID:Nutrition and factors limiting the growth of a methanogenic bacterium (Methanobacterium thermoautotrophicum). 88 84

Four major glycoproteins were extracted by dilute salt solution from procine mitral valvular tissue. Two of these major glycoproteins, procine valve glycoprotein I and porcine valve glycoprotein III, were isolated and purified by fractionation of salt extract with ammonium sulfate followed by column chromatography on DEAE-cellulose. The purified glycoproteins appeared to be homogeneous by polyacrylamide disc electrophoresis in several buffer systems, and by Sephadex filtration. The porcine valve glycoprotein I has a molecular weight of approximately 120000. Isoelectric focusing yielded a single band, pI = 5.8. The glycoprotein contained large amounts of acidic amino acids, and amide nitrogen. The carbohydrate moiety was composed of fucose, mannose, galactose, glucose, glucosamine, and galactosamine in the molar ratio of 5:10:15:12:7:2 per mole of glycoprotein. The second major glycoprotein, porcine valve glycoprotein III, has an approximate molecular weight of 72000. This glycoprotein gives two bands upon analytical isoelectric focusing with isoelectric points of pI = 4.1 and 4.3. Porcine valve glycoprotein III contained large amounts of acidic amino acids and low amounts of amide nitrogen. Its carbohydrate moiety was composed of glucose, galactose, mannose, fucose, glucosamine, and sialic acid in the ratio of 3:3:2:1:4:1 mol/mole of glycoprotein. This glycoprotein was similar to a glycoprotein preparation isolated from porcine aortic intima by P.V. Wagh and B.I. Roberts (1972), Biochemistry 11, 4222.
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PMID:Purification and chemical characterization of salt-extractable glycoproteins from porcine mitral valve. 93 28

The effect of hydrogen on fermentation of lactate, pyruvate, fumarate, and succinate by resting rumen microorganisms has been investigated. Under an atmosphere of nitrogen, lactate was fermented to yield acetate as the major product (85 to 100 mole %) and propionate (0 to 17 mole %) and butyrate (0 to 3%) as secondary products. Under hydrogen, there was increased formation of both propionate and total volatile fatty acids. The amount of propionate increased 4 to 8 times and total volatile fatty acids 2.5 to 3.2 times. Propionate formation was proportional to the hydrogen concentration and reached a maximum at a partial pressure of hydrogen of .2 N/m2. With [2-carbon-14] lactate, propionate was formed via the dicarboxylic acid pathway under both nitrogen or hydrogen. Hydrogen did not affect significantly the fermentation of pyruvate or succinate. With fumarate under hydrogen, propionate and total volatile fatty acids increased 6.8 and 2 times while acetate was unchanged. The mechanism by which hydrogen exerts these effects is discussed in relation to the role of methanogenesis in the rumen.
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PMID:Factors influencing rumen fermentation: effect of hydrogen on formation of propionate. 95 83

Samples of lobster hemocyanin (Homarus americanus) under conditions of reversible reaction between whole (25 S) and half (17 S) molecules have been subjected to accurately known nitrogen pressures in analytical ultracentrifuge cells. A modified pressurization chamber of the type developed by Schumaker and colleagues has been constructed for this purpose. The molecular weight was then determined at the top (liquid-gas) meniscus, by means of the Archibald method. The logarithmic dependence upon pressure of the derived equilibrium constant then gave directly the volume of reaction. Experiments were performed in veronal-citrate buffers at pH 8, where the molar volume of formation of whole (dodecameric) molecules from half molecules appears to be negative, and at pH 8.46 in veronal-citrate buffer in the presence of 0.003 molar free calcium ion, where the molar volume of formation was estimated to be + 390 cm3/mole. In glycine-sodium hydroxide buffer at pH 9.6 containing 0.0047 molar free calcium, the molar volume of formation of whole molecules was estimated to be +120 +/- 70 cm3, corresponding to an estimated difference in partial specific volume between whole molecules and half molecules of only 1.3 (10)-4cm3/gram. The correctness of the sign of this value in glycine buffer has been verified by pressure-jump light-scattering experiments.
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PMID:Volume of reaction by the Archibald ultracentrifuge method (lobster hemocyanin). 96 12

A review of the surface chemistry of bone mineral, hydroxyapatite and amorphous calcium phosphate is presented. Small-angle x-ray scattering and low-temperature nitrogen adsorption measurements show the magnitude of bone mineral surface to range from 100-200 m-2/g; the synthetic hydroxyapatite surface can vary from 25-200 m-2/g, while synthetic amorphous calcium phosphate ranges in surface from 20-60 m-2/g, according to the respective preparation conditions. The magnitude of heats of adsorption of certain small molecules (CO, Ar, N2, H2O, CH3OH) on bone mineral and hydroxyapatite show that these are polarizing surfaces that form strong bonds with polar or polarizable molecules; water is hydrogen-bonded to these surfaces with energies ranging from 23 kcal/mole for low coverage to 11 kcal/mole after two full monolayers; concomitantly, methanol ranges from 24 kcal/mole to 9 kcal/mole after the adsorption of one and a half monolayers. Stearic acid will close-pack perpendicularly on bone apatite surfaces when adsorbed from cyclohexane solution in a way reminiscent of the adsorption of this long, straight-chain molecule on water surface. It is believed that these molecules are hydrogen-bonded to electronegative ions on the apatite surface. Synthetic hydroxyapatite has long been used in chromatographic adsorption columns because of the specific bonding capacity the surfaces have for certain proteins and polynucleotides. The metabolic interrelationship of bone mineral and the body fluids is in great part dependent upon the nature and magnitude of mineral surface. From the surface studies described herein it was suggested that a chemical linkage could exist in bone between the mineral surface and certain free polar groups of collagen.
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PMID:The surface chemistry of bone mineral and related calcium phosphates. 109 77

The effciency of denitrification, or anaerobic respiration, in Pseudomonas denitrificans was investigated, using growth yield as an index. Glutamate was mainly used as the sole source of energy and carbon. In batch culture, the growth yield per mole of electrons transported through the respiratory system under denitrifying conditions was about half that under aerobic conditions. Similar figures were also obtained in chemostat cultures under glutamate-limited conditions. The decrease in growth yield under denitrifying conditions could be due to the restriction of phosphorylation associated with nitrate reduction to nitrogen gas.
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PMID:Growth yield of a denitrifying bacterium, Pseudomonas denitrificans, under aerobic and denitrifying conditions. 115 26


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