CONTROL OF ISOLEUCINE VALINE AND LEUCINE BIOSYNTHESIS .V. DUAL EFFECT OF ALPHA-AMINOBUTYRIC ACID ON REPRESSION AND ENDPRODUCT INHIBITION IN ESCHERICHIA COLI

1. 1. α-Aminobutyric acid was found to cause growth inhibition and derepression of the isoleucine-valine enzymes in Escherichia coli by its effects on valine metabolism. 2. 2. The analog was a potent inhibitor, in vitro and in vivo, of both products of acetohydroxy acid synthetase, the initial enzyme common to isoleucine and valine biosynthesis. The inhibition was non-competitive with respect to the substrate, pyruvate. 3. 3. The transfer of [14C]valine to valine tRNA was strongly inhibited by α-aminobutyric acid. α-Amino[14C]butyric acid was not attached to valine tRNA. 4. 4. It was not possible to distinguish if the observed physiological effects of the analog were due to inhibition of the biosynthesis or activation of valine. © 1968.