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111.
Amino acid transport systems I and III in Neurospora are inhibited by amino acids in the intracellular pool (transinhibition). The transinhibition is system specific. The ability of an amino acid to transinhibit a transport system is highly correlated with its affinity for the system. The significance of the system specificity of transinhibition is discussed. 相似文献
112.
Attractant-Directed Motility in Escherichia coli: Requirement for a Fluid Lipid Phase 总被引:8,自引:4,他引:4 下载免费PDF全文
Attractant-directed motility (chemotaxis) in Escherichia coli has an absolute requirement for a fluid membrane. No such requirement was detected for motility per se. 相似文献
113.
Summary Uranyl sulphate (0.2–0.9 mM) inhibited ferrous iron oxidation by growing cultures ofThiobacillus ferrooxidans. The addition of 5–100 mM uranium to the cultures caused immediate cessation of carbon dioxide fixation, rapid loss of viability
and gradual depression of ferrous iron oxidation. Virtually no uranium was found in washed cells grown in the presence of
subtoxic to toxic amounts of uranyl sulphate. Uranium-poisoned organisms appeared plasmolyzed in electron micrographs. Cultures
tolerant to 5 mM UO2
2+ were develoepd by successive subculturing in increased uranium concentrations. The tolerance was maintained during subculturing
in uranium-free medium. Frequency of mutants resistant to 1.0 and 1.5 mM UO2
2+ was 1 per 1.3×106 and 1 per 9.0×108, respectively. The frequency was increased in the presence of 15–150 mM nickel, zinc and manganese. In liquid cultures, bivalent
cations and EDTA alleviated the toxicity of 2 mM uranyl sulphate. 相似文献
114.
115.
1. Pea-seed phosphofructokinase was purified 27-fold by a combination of fractionation with ethanol and ammonium sulphate. Under the conditions of assay, the enzyme was strongly inhibited by phosphoenolpyruvate. This inhibition was reversed by increasing the concentration of fructose 6-phosphate or magnesium chloride, or by lowering the ATP concentration. 2. Citrate, ADP and AMP inhibited phosphofructokinase and increased the sensitivity to phosphoenolpyruvate inhibition. Sulphate and inorganic phosphate stimulated the enzyme activity and decreased the sensitivity to phosphoenolpyruvate. 3. In the presence of inorganic phosphate and low concentrations of ATP, inhibition by phosphoenolpyruvate ceased and phosphoenolpyruvate became stimulatory. 4. The possible significance of these results in the control of plant carbohydrate metabolism is discussed. 相似文献
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D. P. Kelly 《Archives of microbiology》1967,58(2):99-116
Summary Cultures of Thiobacillus neapolitanus strain C assimilate 14C-labelled acetate and aspartate. Both carbon atoms of acetate are incorporated, and 25% of the cell carbon can arise from acetate. Aspartate-14C contributes 4–5% of the cell carbon, and is found in pyrimidines and in protein as aspartate and its related amino acids. Acetate-14C contributes to lipid, glutamate, arginine, proline and leucine, but not to aspartate. Acetate assimilation by washed organisms requires carbon dioxide and energy from thiosulphate oxidation. Degradation of 14C-glutamic acid from acetate-14C-labelled bacteria; the accumulation of 14C-citrate in the presence of fluoroacetate and [14C] acetate; short-term kinetic experiments on acetate-14C turnover; and the demonstration of citrate synthesis by cell-free extracts all indicate glutamate synthesis from -ketoglutarate formed by reactions of the tricarboxylic acid cycle. The cycle is believed to be incomplete, probably not proceeding further than -ketoglutarate, and functions as a glutamate-synthesising system, using oxaloacetate derived solely from carbon dioxide fixation. Malate synthase (and the glyoxylate cycle) appear to be insignificant in the metabolism, but extracts did form citramalate from acetate and pyruvate. 相似文献