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81.
Determination of the Carbon-Bound Electron Composition of Microbial Cells and Metabolites by Dichromate Oxidation 总被引:5,自引:3,他引:2 下载免费PDF全文
The applicability of the silver sulfate-acid dichromate oxidation (chemical oxygen demand) method for determining the carbon-bound electron compositions of microbial cells, substrates, and metabolic by-products was evaluated. An approach for approximating the carbon-bound electron composition of microbial cells from CHN data is also presented. Ten aliphatic and aromatic carboxylic acids, 17 amino acids, and 8 sugars generally gave 96 to 101% (mainly ≥98%) recovery with 0.0625 N dichromate (digestion mixture of 10 ml of sample-10 ml of 0.25 N dichromate-20 ml of Ag2SO4-amended concentrated H2SO4). Recoveries of nicotinic acid (5%) and methionine (65%) were incomplete; arginine (125%) and two purine and three pyrimidine bases (105 to 120%) were overestimated. The validity of 0.0625 N dichromate for determining the carbon-bound electron composition of bacterial cells was supported by theoretical analysis of the carbon-bound electron composition of hypothetical bacterial cell material (defined monomer composition) and by the compatibility of elemental and dichromate oxidation-derived carbon-bound electron compositions of typical bacterial cells. 相似文献
82.
83.
Synopsis The interaction of fluctuating water level and the Long Point topography is discussed with regard to the formation of lake-shore lagoons and their subsequent invasion by fishes. The species composition of fish communities in these lagoons was determined by 12 collections from lagoons (23 m2 to 25 ha) which yielded 33 fish species. The relationship of the number of fish species to lagoon area was lognormal; that is, with increasing lagoon area the number of species rose rapidly at first but soon decreased sharply, probably limited by the number of species capable of surviving in the habitat. The marked effect of area on species number in small lagoons is considered in the context of a hypothetical seasonal pattern of occasional invasion and continuous extinction.A sequence of reproductive guilds was found. In beach lagoons psammophils and lithophils were dominant. In a large vegetated lagoon in the interior phytophils and speleophils were dominant. This sequence was paralleled by an increase in the proportion of guarding and nesting species in the communities. The sequence was disrupted in the small interior lagoons where adaptations for survival were more important than reproductive strategy. 相似文献
84.
1. When Triton-filled lysosomes from rat liver are incubated for up to 50min at 37 degrees C, pH7.4, in 0.25m-sucrose, no loss of latency of N-acetyl-beta-glucosaminidase or p-nitrophenyl phosphatase occurs unless the incubated lysosomes are cooled to approx. 15 degrees C. 2. It is suggested that a phase change takes place in the incubated lysosomal membranes on cooling; it starts at approx. 15 degrees C and probably is not complete at 0 degrees C. 3. Incubation of the lysosomes causes an increased potential for loss of latency of the lysosomal enzymes. This potential is not fully expressed at elevated temperature (e.g. 37 degrees C), but is expressed on cooling. 4. The increase at elevated temperature in potential for loss of latency exhibits biphasic kinetics, with an initial rapid phase followed by a slower phase, which is linear with respect to time. The extra loss of latency resulting from the rapid phase in proportional to the temperature of the incubation. 5. Arrhenius plots of the increase is potential for loss of latency during the slow phase for N-acetyl-beta-glucosaminidase and p-nitrophenyl phosphatase exhibit marked deviations from linearity beginning at approx. 15 degrees C. This suggests that the increase in potential for loss of latency is affected by a phase change that occurs around this temperature. 6. Activation energies for the increase in potential for loss of latency at and above 22 degrees C are 53.1+/-5.4kJ/mol (12.7+/-1.3kcal/mol) for N-acetyl-beta-glucosaminidase and 45.2+/-7.5kJ/mol (10.8+/-1.8kcal/mol) for p-nitrophenyl phosphatase. It is postulated that these energies reflect enzymic action, the products of which cause loss of latency to occur on cooling. 相似文献
85.
Superoxide dismutase (SOD) activity in hypoxic mammalian systems 总被引:2,自引:0,他引:2
86.
(1) The effects of changes in the intramitochondrial volume, benzyl alcohol treatment and calcium-induced mitochondrial aging on the behaviour of liver mitochondria from control and glucagon-treated rats are reported. (2) The stimulatory effects of glucagon on mitochondrial respiration, pyruvate metabolism and citrulline synthesis could be mimicked by hypo-osmotic treatment of control mitochondria and reversed by calcium-induced aging of mitochondria or by treatment with 20 mM benzyl alcohol. Hypo-osmotic treatment increased the matrix volume whilst aging but not benzyl alcohol decreased this parameter. (3) Liver mitochondria from glucagon and adrenaline-treated rats were shown to be less susceptible to damage by exposure to calcium than control mitochondria and frequently showed slightly (15%) elevated intramitochondrial volumes. (4) Aging, benzyl alcohol and hypo-osmotic media increased the susceptibility of mitochondria to damage caused by exposure to calcium. (5) Glucagon-treated mitochondria were less leaky to adenine nucleotides than control mitochondria. (6) These results suggest that glucagon may exert its action on a wide variety of mitochondrial parameters through a change in the disposition of the inner mitochondrial membrane, possibly by stabilisation against endogenous phospholipase A2 activity. This effect may be mimicked by an increase in the matrix volume or reversed by calcium-dependent mitochondrial aging. 相似文献
87.
The interaction of cholesterol with the glycerol backbone segments of phospholipids was studied in bilayers of phosphatidylethanolamine containing equimolar amounts of cholesterol. Glycerol selectively deuterated at various positions was supplied to the growth medium of Escherichia coli strain 131 GP which is defective in endogeneous glycerol synthesis. The procedure enables the stereospecific labeling of the three glycerol backbone segments of the membrane phospholipids. Phosphatidylethanolamine with wild-type fatty acid composition was purified from E. coli cells and deuterium magnetic resonance spectra were obtained either from dispersions of pure phosphatidylethanolamine or from equimolar mixtures of phosphatidylethanolamine with cholesterol. For comparative purposes 1,2-di[9,10-2H2]elaidoyl-sn-glycero-3-phosphoethanolamine and [3-α-2H]cholesterol were synthesized in order to monitor the behavior of the fatty acyl chains and of the cholesterol molecule itself. For all deuterated segments the deuterium quadrupole splittings as well as the deuterium spin-lattice (T1) relaxation times were measured as a function of temperature. The glycerol backbone was found to be a remarkably stable structural element of the phospholipid molecule. The quadrupole splittings of the backbone segments changed only by at most 2 kHz upon incorporation of 50 mol % cholesterol. This was in contrast to the fatty acyl chains where the same amount of cholesterol increased the quadrupole splitting by more than 20 kHz. The glycerol segments exhibited the shortest T1 relaxation times of all CH2 segments indicating that the glycerol backbone is the slowest motional moiety of the lipid molecule. Addition of cholesterol has no effect on the backbone motion but the fast reorientation rate of the trans-double bonds in 1,2-dielaidoyl-sn-glycero-3-phosphoethanolamine is increased dramatically. 相似文献
88.
89.
Several aspects of infanticide, including effects of social status, prior sexual experience, and the basis for discrimination between related and unrelated young, were examined in Swiss-Webster laboratory mice (Mus musculus). Strange males introduced into the female's cage for 24 h on day 1 postpartum significantly reduced pup survival whereas the introduction of sires did not. Direct observations of infanticide were frequent, and the motor patterns used by males to kill pups are described. Males killed their own offspring when those young were in the nest of a strange female, whereas most males did not kill unrelated young in the nest of a familiar female. Thus, past association with the mother appears to be the single most important factor mediating male discrimination of young. Prior contact with a specific female's urine reduced a male's propensity for subsequently killing her young. The act of copulation itself also reduced infanticide. Infanticidal behaviour was correlated with the male's social status: most dominant males killed unrelated pups, whereas none of the subordinates engaged in infanticide. These results are discussed in terms of the population biology of this species. 相似文献
90.
Peroxynitrite oxidation of sulfhydryls. The cytotoxic potential of superoxide and nitric oxide. 总被引:46,自引:0,他引:46
Peroxynitrite anion (ONOO-) is a potent oxidant that mediates oxidation of both nonprotein and protein sulfhydryls. Endothelial cells, macrophages, and neutrophils can generate superoxide as well as nitric oxide, leading to the production of peroxynitrite anion in vivo. Apparent second order rate constants were 5,900 M-1.s-1 and 2,600-2,800 M-1.s-1 for the reaction of peroxynitrite anion with free cysteine and the single thiol of albumin, respectively, at pH 7.4 and 37 degrees C. These rate constants are 3 orders of magnitude greater than the corresponding rate constants for the reaction of hydrogen peroxide with sulfhydryls at pH 7.4. Unlike hydrogen peroxide, which oxidizes thiolate anion, peroxynitrite anion reacts preferentially with the undissociated form of the thiol group. Peroxynitrite oxidizes cysteine to cystine and the bovine serum albumin thiol group to an arsenite nonreducible product, suggesting oxidation beyond sulfenic acid. Peroxynitrous acid was a less effective thiol-oxidizing agent than its anion, with oxidation presumably mediated by the decomposition products, hydroxyl radical and nitrogen dioxide. The reactive peroxynitrite anion may exert cytotoxic effects in part by oxidizing tissue sulfhydryls. 相似文献