Incubation of aerobic cultures of Saccharomyces cerevisiae with high concentrations of glucose leads to the repression of heme biosynthesis [I] and to the accumulation of prototetrahydroporphyrin IX, a pigment with an absorption maximum at 503 nm,

No abstract

No abstract

A comparison of the extracellular products of glucose metabolism during aerobic exponential growth of Escherichia coli showed that a streptomycin-dependent strain produced large amounts of L-valine while only trace amounts of this amino acid were produced by streptomycinsensitive strains. A further difference between sensitive and dependent mutants was the production by the latter of lactic acid when the gas phase was changed from air to nitrogen. Resistant cultures grown in antibiotic-free medium were similar to sensitive cultures, but when dihydrostreptomycin was added, the resistant organism produced lactic and pyruvic acids. Three strains of streptomycin-sensitive E. coli accumulated pyruvic acid from glucose oxidation in the presence of concentrations of dihydrostreptomycin which inhibited multiplication. Further evidence is thus provided to implicate reactions of pyruvate as being of significance in the mechanism of action of streptomycin.

Acetolactate formation in Escherichia coli B results from the activity of a single system, acetohydroxy acid synthetase, which has a pH optimum of 8.0 and is sensitive to end-product inhibition by l-valine. Acetohydroxy acid synthetase was found to be subject to catabolite repression, and the nature and concentration of the carbon source had a greater effect on the formation of the enzyme than had the known end products (valine, isoleucine, leucine and pantothenate) of the biosynthetic pathways of which this enzyme is a member. The results suggest that acetohydroxy acid synthetase may play an amphibolic role in E. coli B.