Inhibition of Escherichia coli isoleucine biosynthesis by isoleucine tetrazole

Growth of a derivative of Escherichia coli K-10 was strongly inhibited by 2 times 10(-4) M L-5(1-amino-2-methylbutyl)-tetrazole (isoleucine tetrazole). Growth inhibition was reversed by isoleucine, threonine, glycyl-L-isoleucine, or glycyl-L-threonine, and, in a valine-resistant mutant, by L-valine. Partial reversal of growth inhibiton was effected by L-leucine, L-methionine, or L-homoserine. The tetrazole inhibited the activity of the biosynthetic threonine deaminase (EC 4.2.1.16 L-threonine hydrolyase [deaminating]), the inhibition being relieved by L-valine. The tetrazole also inhibited isoleucyl-transfer ribonucleic acid (tRNA) synthetase (EC 6.1.1.5 L-isoleucine: tRNA ligase [adenosine monophosphate]), but was without effect on the activities of alpha-isopropylmalate synthetase or acetohydroxy acid synthetase. One class of isoleucine tetrazole-resistant mutants produced biosynthetic threonine deaminases which were no longer subject to feedback inhibition by either isoleucine or the tetrazole.