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1.
(1) +/electron acceptor ratios have been determined with the oxidant pulse method for cells of denitrifying Paracoccus denitrificans oxidizing endogenous substrates during reduction of O2, NO?2 or N2O. Under optimal H+-translocation conditions, the ratios , , for reduction to N2 and for reduction to N2O were 6.0–6.3, 4.02, 5.79 and 3.37, respectively. (2) With ascorbate/N,N,N′,N′-tetramethyl-p-phenylenediamine as exogenous substrate, addition of NO?2 or N2O to an anaerobic cell suspension resulted in rapid alkalinization of the outer bulk medium. , for reduction to N2 and for reduction to N2O were ?0.84, ?2.33 and ?1.90, respectively. (3) The ratios, mentioned in item 2, were not altered in the presence of and the triphenylmethylphosphonium cation. (4) A simplified scheme of electron transport to O2, NO?2 and N2O is presented which shows a periplasmic orientation of the nitrite reductase as well as the nitrous oxide reductase. Electrons destined for NO?2, N2O or O2 pass two H+-translocating sites. The acceptor ratios predicted by this scheme are in good agreement with the experimental values. 相似文献
2.
The proximal colon of the new-born pig maintains a stable short-circuit current which is partly dependent upon the presence of methionine. This interaction between methionine and short circuit current shows Michaelis- Menten knetics with a of 0.24 mM and a of 27 μA·cm?2. The net flux of methionine to the serosal surface of proximal colons also shows a hyperbolic relation to the external concentration of methionine (; ). The proximal colon concentrates methionine within its epithelium giving a mucosal to medium ratio of (90 min incubation in 1 mM methionine).The ability of the colon to transport methionine across and concentrate methionine within its mucosa is maintained for at least 24 h after birth. Colonic transport of amino acids could be physiologically important in the pig, where the immediate post-natal transfer of immune globulins has been shown to cause a temporary inhibition of normal intestinal function. 相似文献
3.
For two N-species assemblages A, B with specific proportionate abundances of the ith species ai, bl respectively, we consider the equality . The left-hand term is known as Sanders' minimum faunal abundance value, while the right side is referred to as Whittaker's similarity index. Both measures are commonly used in community studies. Equality between these two measures obtains only when proportionate abundances are utilized. We develop equivalent formulation which is valid for absolute abundance data, reduces to the Sanders-Whittaker equality when proportionate abundance data are employed, and is more sensitive to differences in species abundance distributions. Namely, we show that , where , and the a's, b's c's are as defined above. 相似文献
4.
A theoretical study of calcium entry in nerve terminals, with application to neurotransmitter release 总被引:4,自引:0,他引:4
In his study of a kin selection model for the evolution of workers' behavior in an incipiently social insect, Craig (1979) found that the haplodiploid mode of sex determination, combined with a female-biased sex ratio, cannot accelerate an evolutionary trend toward eusociality. This seems to contradict to Hamilton's (1964) theory. It is my intention to prove that Craig's result is due to the dependence of relative reproductive success in each sex on the sex ratio of a population. The oviposition of unfertilized eggs by workers is indispensable, in primitive stages in the evolution of eusociality, for maintaining the relative reproductive success of a female. Assuming that workers control the sex ratios, we can distinguish the following three evolutionary phases in accordance with the ratio (the ratio of the number of the queen's second brood to that of the progeny laid by workers derived from the same nest). During Phase 1 in which < , the reproductive successes of a male and a female are equal, and Hamilton's rule holds. In Phase 2 in which , the queen produces females, and workers oviposit males. As increases, the sex ratio in the whole population becomes female-biased and relative reproductive success of a male increases. In Phase 3 in which N2/N10 >, the queen lays some male eggs in addition to female eggs. The sociality threshold ()crit the minimum value of the benefit/cost ratio leading to the evolution of altruism, is on Phase 1. It rises threefold as N2/N10 increases in Phase 2, and, in Phase 3, it is twice as high as that in a diploid species. The anatomical and physiological characteristics of workers must have been so developed that they are efficient in helping activities after the beginning of eusociality. The evolutionary process before the beginning of helping behavior is also discussed. The egg laying by unmated females, which stay their mother's nest, seems to have been an important preadaptation for the evolution of eusociality in Hymenoptera. 相似文献
5.
Conversion of thyroxine to 3,3',5'-triiodothyronine (reverse-T3) by a soluble enzyme system of rat liver 总被引:3,自引:0,他引:3
R R Cavalieri L A Gavin F Bui F McMahon M Hammond 《Biochemical and biophysical research communications》1977,79(3):897-902
Infrared spectra of N2O in a variety of solvents and in the brain of a dog under typical conditions of halothane-N2O anesthesia have been determined. The appearance or disappearance of N2O in the brain was readily followed as N2O was administered or withdrawn. The sites in brain were of two major types; one, with ν3 = 2229.8 ± 0.4 cm?1 and , is rather like the polar site in water and the other, with ν3 = 2216.8 ± 0.8 cm?1 and , is non-polar and is probably associated with membrane lipid. The significant variations in the antisymmetric stretch (ν3) of N2O as the polarity and other properties of the medium (solvent) vary make possible the characterization of sites occupied by this anesthetic. 相似文献
6.
E G Bliznakov Y P Wan D Chang K Folkers 《Biochemical and biophysical research communications》1978,80(3):631-636
The stability of mouse uterine cytosol receptor-[3H]estradiol complex was evaluated in the presence of neutral salts of the Hoffmeister series. Marked increases in the rate of dissociation of the complex were observed with the more chaotropic anions (SCN?, , , Br?), and the effects of these ions were greater at lower temperatures, where water assumes a more rigid structure. At higher temperatures F? and CH3COO?, which tend to stabilize water structure, led to retardation of the rate of dissociation of the hormone-receptor complex. There was essentially no change in steroid specificity in the presence of the markedly chaotropic salts. The perturbation of water structure adjacent to the steroid binding site is a factor to be considered in the isolation of steroid receptor complexes. 相似文献
7.
Hiroshi Watari Yoshinori Isogai Hiroyasu Nlshikawa 《Journal of theoretical biology》1980,83(2):209-214
The maximum slope of the plot, appearing in the paper of Watari & Isogai (1976), was derived algebraically as a function of allosteric constants c and αmor βm (= cαm), and the relation between L, c, and αmor βm, was also obtained, where are concentrations of unligated R and T states respectively, KRand KT are microscopic dissociation constants, and Fm is the ligand concentration at the maximum slope of the plot. When the maximum slope is increased by one, the value becomes Hill constant, n. Nomographs which enable easier estimation of allosteric constants, L and c, were constructed from the two given values, the maximum slope of the plot, n ? 1, and αmor βm, in the cases where the maximum number of ligands, N, was 2 and 4. In the nomograph, log c is plotted against log L2cN keeping the value of the maximum slope of the plot and that of αmor βm constant. These nomographs show that the representation is symmetrical in the cases of L2cN > 1 and L2cN < 1. 相似文献
8.
In order to test the question if a pool of lipophilic ions may exist in black lipid membranes which cannot be detected by electrical relaxation measurements we have performed simultaneously measurements of the optical absorption of a lipophilic ion. The absorbance of membrane-bound dipicrylamine at 410 nm was measured with a sensitive spectrophotometer which can detect absorbance changes . A minimal concentration of about 6 · 1011 dipicrylamine ions per cm2 of the membrane could be detected with this instrument. The dipicrylamine concentration in the membrane obtained with the optical method is compared with the concentrations obtained from simultaneous electrical relaxation measurements. and agreed at low dipicrylamine concentrations (10?8–10?7 M in the aqueous phase) and showed saturation at higher concentrations (up to 5 · 10?6 M). In the saturation range was maximally four times higher than . The significance of this difference is discussed together with general aspects of the saturation phenomenon. 相似文献
9.
David J.T. Porter Noel G. Rudie Harold J. Bright 《Archives of biochemistry and biophysics》1983,225(1):157-163
The reactivities of the nitro analogs of the substrates of adenylosuccinate synthetase and adenylosuccinate lyase, the enzymes which catalyze the penultimate and last step, respectively, in the pathway for AMP biosynthesis have been examined. Alanine-3-nitronate, an aspartate analog, was a substrate for the synthetase from Azotobacter vinelandii, having a which was ~30% that for aspartate. The product of this reaction was N6-(l-1-carboxy-2-nitroethyl)-AMP. Of nine other substrate analogs tested, only cysteine sulfinate (having 5.5% of the activity of aspartate) was reactive. These results demonstrate the strict requirement of the synthetase for a negatively charged substituent, with a carboxylate-like geometry, at the β-carbon of the α-amino acid substrate. The lyase, purified to homogeneity from brewer's yeast by a new procedure, did not utilize N6-(l-1-carboxy-2-nitroethyl)-AMP as a substrate. However, the nitronate form of this analog was a good inhibitor of the lyase ( when compared to adenylosuccinate), suggesting that it mimics a carbanionic intermediate in the reaction pathway. The avid binding of bromphenol blue by the lyase (i = 0.95 μM) was used for active site titrations and for displacement of the enzyme, in the purification protocol, from blue Sepharose. 相似文献
10.
Base-group specificity at the primary recognition site of ribonuclease T1 for minimal RNA substrates
Frederick G. Walz Harry L. Osterman Charissa Libertin 《Archives of biochemistry and biophysics》1979,195(1):95-102
Kinetic studies on the RNase T1-catalyzed transesterification of 12 dinucleoside monophosphates, Np1N2 (N1 = A, C, and U; N2 = A, C, G, and U) at pH 5, 25 °C, and 0.2 m ionic strength, revealed that the catalytic efficiency () for GpN substrates (H. L. Osterman, and F. G. Walz, Jr., 1978, Biochemistry, 17, 4142) was ~106-fold greater than corresponding ApNs and at least 108-fold greater than corresponding CpNs and UpNs. The catalytic activity with ApN substrates survives phenol extraction which indicates (along with other criteria) that it is intrinsic to RNase T1 and is not due to trace contamination by other nucleases. Circumstantial evidence is presented which suggests that homologous GpN and ApN substrates bind productively at different sites on the enzyme. The results of steady-state kinetic studies of RNase T1 with IpNs (N = C and U) were compared with those for GpNs and indicated that the primary effect of the guanine 2-NH2 group is to enhance substrate binding at the primary recognition site by ~2.6 kcal/mol. Values of () showed the order NpC > NpU (N = A, G, and I) which evidences the existence of a subsite for the leaving nucleoside group that prefers cytidine: interactions at this subsite are reflected in kcat rather than Km. 相似文献
11.
(1) Na+ currents and Na+-current fluctuations were measured in myelinated frog nerve fibres at 15°C during 7.7 ms depolarizations to . (2) The conductance γ of a single Na+ channel and the number of channels per node were calculated from ensemble average values of the mean Na+ current and the variance of Na+-current fluctuations. (3) For a hyperpolarizing holding potential of the mean values of the channel conductance and number were and . (4) After changing the holding potential to the resting potential () the conductance γ increased by a factor of 1.37 whereas the number decreased by a factor of 0.60. (5) Addition of 8 nM tetrodotoxin at a holding potential of increased γ by a factor of 1.55 and reduced by a factor of 0.25. (6) The increase of the channel conductance at reduced channel numbers suggests negative cooperativity between Na+ channels in the nodal membrane. 相似文献
12.
John A. Jacquez 《生物化学与生物物理学报:生物膜》1973,318(3):411-425
The Michaelis-Menten parameters, and of the initial 1-min fluxes of uptake of l-phenylalanine and of α-aminoisobutyric acid were determined for extracellular concentrations of Na+ ranging from 0.5 to 110 mequiv/l for Ehrlich ascites tumor cells. The maximal initial flux, , decreased with decrease in extracellular Na+ for both α-aminoisobutyric acid and phenylalanine but the for α-aminoisobutyric acid increased markedly as the Na+ concentration fell whereas the for phenylalanine decreased. Cycloleucine behaved like phenylalanine.The data provides strong evidence that the Na+-independent flux of phenylalanine is an exchange diffusion flux that can be varied by changing the intracellular level of amino acids such as phenylalanine. For phenylalanine, cyclolcucine, and methionine this exchange diffusion flux appears to be additive with the Na+-dependent initial flux. α-Aminoisobutyric acid also has an exchange diffusion that is Na+-independent but it has a high and is not additive with the Na+-dependent flux. 相似文献
13.
ADP and Pi-loaded membrane vesicles from l-malate-grown Bacillus alcalophilus synthesized ATP upon energization with . ATP synthesis occurred over a range of external pH from 6.0 to 11.0, under conditions in which the total protonmotive force was as low as ?30 mV. The phosphate potentials (ΔGp) were calculated to be 11 and 12 kcal/mol at pH 10.5 and 9.0, respectively, whereas the values in vesicles at these two pH values were quite different (?40 ± 20 mV at pH 10.5 and ?125 ± 20 mV at pH 9.0). ATP synthesis was inhibited by KCN, gramicidin, and by N,N′-dicyclohexylcarbodiimide. Inward translocation of protons, concomitant with ATP synthesis, was demonstrated using direct pH monitoring and fluorescence methods. No dependence upon the presence of Na+ or K+ was found. Thus, ATP synthesis in B. alcalophilus appears to involve a proton-translocating ATPase which functions at low . 相似文献
14.
Robert P. le Borgne 《Journal of experimental marine biology and ecology》1979,37(2):127-137
Respiration (O), ammonium (NH4), phosphate (PO4), total nitrogen (NT) and phosphorus (PT) excretions were measured on mixed zooplankton during 3-, 6-, 9-, 12-, 21-, and 24-h incubation periods at 20–23 C. The excretion rates of PO4, NT. and PT decrease during a 21-h period, while rates of respiration and excretion of NH{IN4} are constant. The percentage of inorganic nitrogen excreted increases regularly from 3 h (30–40% of total nitrogen) to 21 h (70–80%) and it could be either due to a bacterial activity which was measured or to a decrease with time of organic nitrogen excreted because of starvation. , , , and ratios increase during the first 9 h of incubation; the percentage of inorganic phosphorus excreted is higher at the very beginning and then remains constant from 6 to 24 h. and ratios are constant during a 24-h term, which makes them useful metabolic indexes. 相似文献
15.
N-Phenylhydroxylamine is oxidized in aqueous phosphate buffer to nitrosobenzene, nitrobenzene, and azoxybenzene. Degradation is O2 dependent and shows general catalysis by (k1 = 2.3 M?2 sec?1) and (k2 = 2.3 × 105M?2 sec?1) or kinetically equivalent terms. Evidence is presented suggesting the intermediacy of a highly reactive species leading to these products. 相似文献
16.
The uptake of d-glucose, 2-aminoisobutyric acid and glycine was studied with intestinal brush border membrane vesicles of a marine herbivorous fish: Boops salpa. The uptake of these three substances is stimulated by an Na+ electrochemical gradient (). For glucose, an increase of the electrical membrane potential generated by a concentration gradient of the liposoluble anion, SCN?, increases the Na+-dependent transport. This responsiveness to the membrane potential was confirmed by valinomycin. Differently from glucose, uptake of glycine and 2-aminoisobutyric acid requires, besides the Na+ gradient, the presence of Cl? on the external side of the vesicles. In the absence of Cl?, amino acid uptake is not stimulated by the Na+ gradient and is not influenced by an electrical membrane potential generated by SCN? gradient () or by a K+ diffusion potential (). This Cl? requirement differs from the Na+ requirement, since a Cl? gradient () does not result in an accumulation of glycine or 2-aminoisobutyric acid similar to that produced by an Na+ gradient. 相似文献
17.
The interaction of |CnH2n+1N+(CH3)3| · I? (n = 3, 6, 9, 12, 14, 16 or 18) with egg-yolk phosphatidylcholine-water dispersions has been studied by 31P-NMR spectroscopy. It is shown that the effective anisotropy of 31P chemical shift (?Δσeff) of the lamellar phospholipid liquid-crystalline phase Lα increases with increasing concentration and alkyl chain length of the drug. Addition of or |C9H19N+(CH3)3|·I? to the phospholipid-water dispersion at a molar ratio ammonium salt:phospholipid > 0.8 induces in the dispersion a structure with an effective isotropic phospholipid motion. This structure is unstable and slowly transforms into the hexagonal phase. These effects have not been observed in phospholipid-water dispersions mixed with the ammonium derivatives with the longer alkyl chains n 12, 14, 16 or 18. It is proposed that these results might explain the effects of the investigated drugs on the nerve, muscle and bacterial cells. 相似文献
18.
Presteady-state kinetic studies of α-chymotrypsin-catalyzed hydrolysis of a specific chromophoric substrate, N-(2-furyl)acryloyl-l-tryptophan methyl ester, were performed by using a stopped-flow apparatus both under [E]0 ? [S]0 and [S]0 ? [E]0 conditions in the pH range of 5–9, at 25 °C. The results were accounted for in terms of the three-step mechanism involving enzyme-substrate complex (E · S) and acylated enzyme (ES′); no other intermediate was observed. This substrate was shown to react very efficiently, i.e., the maximum of the second-order acylation rate constant (. The limiting values of Ks′ (dissociation constant of E · S), K2 (acylation rate) and k3 (deacylation rate) were obtained from the pH profiles of these parameters to be 0.6 ± 0.2 × 10?5 m, 360 ± 15 s?1 and 29.3 ± 0.8 s?1, respectively. Likewise small values were observed for Ki of N-(2-furyl)-acryloyl-l-tryptophan and N-(2-furyl)acryloyl-d-tryptophan methyl ester and Km of N-(2-furyl)acryloyl-l-tryptophan amide. The strong affinities observed may be due to intense interaction of β-(2-furyl)acryloyl group with a secondary binding site of the enzyme. This interaction led to a value lower than unity, i.e., the rate-limiting process of the acylation was the association, even with the relatively low k2 value of this methyl ester substrate, compared to those proposed for labile p-nitrophenyl esters. 相似文献
19.
20.
The immobilization of Rhodopseudomonas capsulata chromatophores by entrapment in an alginate gel is described. Alginate beads were prepared with Ba2+, Sr2+ and Ca2+ as gel-forming agents and compared for their mechanical strength, chemical resistance against disruption by phosphate-induced swelling, and yield of photophosphorylation activity. Barium alginate beads proved to have better physico-chemical properties than the more commonly used calcium alginate beads. After embedding in barium alginate gel, R. capsulata chromatophores retained a high yield (up to 70%) of their photophosphorylation capacity. Alginate entrapment did not cause a large increase in the Michaelis constant for ADP and phosphate, the substrates of adenosinetriphosphatase (ATPase). These constants were and for free chromatophores and and for chromatophores entrapped in barium alginate gel. However, embedding gave no additional protection against rapid inactivation of chromatophores upon storage at 3°C. Preliminary results with a batch reactor for continuous ATP regeneration are presented. The barium alginate method has two features which are not generally encountered at the same time, extremely mild conditions for entrapment and excellent physical properties of the gels beads, which make this method a suitable tool for the construction of bioreactors with immobilized cells or organelles. 相似文献