REGULATION OF ACETOHYDROXY ACID SYNTHETASE IN STREPTOMYCIN-DEPENDENT ESCHERICHIA COLI K-12

Abstract

The formation of acetohydroxy acid (AHA) synthetase in streptomycin-dependent Escherichia coli K-12 as a function of antibiotic (dihydrostreptomycin) concentration can be expressed by a Michaelis constant (KM = 2 × 10−4M). Valine exerts end-product repression (partial) of AHA synthetase in competition with the positive regulatory effect of dihydrostreptomycin. In dependent E. coli K-12, growth (as measured by optical density increase) correlated closely with the formation of AHA synthetase. The observed positive effect of dihydrostreptomycin on AHA synthetase formation suggests that derepression of this enzyme may be obligatory in antibiotic-dependent cells.