REPRESSION OF REDUCTOISOMERASE IN ESCHERICHIA COLI BY L-VALINE

Abstract

The reductoisomerase in the biosynthetic pathway leading to isoleucine and valine is represed by L-valine, but not by isoleucine in Escherichia coli K-12. The mode of repression in a methionine-requiring mutant is different from that of wild type. The reductoisomerase of the methionine-requiring mutant and its derivatives, the isoleucine-valine requiring mutants, is repressed by valine to a low level, if the molar ratio of L-isoleucine to L-valine in the medium is below 1. On the other hand, the synthesis of the reductoisomerase in the wild-type strain is gradually decreased by increasing amounts of L-valine in media containing a constant amount of L-isoleucine. The repression by L-valine is specific for the reductoisomerase and independent of the induction of β-galactosidase.