REGULATION OF ACETOHYDROXY ACID SYNTHETASE IN STREPTOMYCIN-DEPENDENT ESCHERICHIA COLI

Abstract

The formation of acetolactate from pyruvate by extracts of streptomycin-dependent Escherichia coli was inhibited, competitively, by L-valine, thus establishing the potential in the dependent mutant for regulation of the activity of acetohydroxy acid synthetase through end-product inhibition. Furthermore, the level of acetohydroxy acid synthetase was decreased in streptomycin-dependent E. coli by growth in minimal medium to which had been added the end products of the biosynthetic pathways initiated by this enzyme, thus establishing the potential in dependent cells for regulation of acetohydroxy acid synthetase through repression. In contrast, the specific activity of acetohydroxy acid synthetase in extracts of streptomycin-dependent E. coli increased in proportion to the concentration of antibiotic (dihydrostreptomycin) present in the medium during growth, thereby indicating a positive regulatory effect of dihydrostreptomycin on the formation of this enzyme. The formation of two enzymes used as monitors, glucokinase, and glutamic dehydrogenase, was not affected by variation in antibiotic concentration.