Repression of Acetolactate Synthetase by Glucose inAerobacter aerogenes

Abstract

The effect of various carbon sources on the formation of acetolactate synthetase (ALS) was investigated with Aerobacter aerogenes No. 19–35. ALS which has a pH optimum of 6.0 and is insensitive to end-product inhibition by valine, was found to subject to catabolite repression by glucose. The catabolite repression was dependent on phosphate deficiency. In contrast, in Aerobacter aerogenes I–12, isoleucine-less mutant, acetohydroxy acid synthetase (AHASr) which has a pH optinum of 8.0 and is insensitive to valine, was resistant to catabolite repression. Since both insensitive enzymes to valine inhibition was not subject to dual control. “Glucose-effect” of ALS was released by addition of orthophosphate and 6-mercaptopurine or by anaerobic culture. It was revealed that accumulation of valine was due to operation of the regulatory mechanism releasing catabolite repression of insensitive enzyme. It was suggested that regulation of enzymes involved in valine biosynthetic pathway was closely concerned with glucose metabolism.