The reversal of the inhibitory activity of l-penicillamine by branched chain amino acids

1. 1. l-Penicillamine, the β,β-dimethyl analogue of cysteine, is an extremely weak antagonist of the utilization of the vitamin B 6 complex by S. carlsbergensis. 2. 2. l-Penicillamine inhibits the growth of E. coli 9723. The 17-h growth-inhibitory activity is reversed completely by either isoleucine, valine, leucine or methionine, amino acids that are analogous in chemical structure to l-penicillamine. Isoleucine is the most effective. Other naturally occurring amino acids and vitamins do not reverse this inhibitory activity. The data suggest that the site of action of l-penicillamine in E. coli is one or more enzymes involved specifscally in the metabolism of the branched chain amino acids isoleucine, valine and leucine. 3. 3. The metabolites that reverse the growth-inhibitory effects of l-penicillamine in E. coli and in the rat differ, suggesting a difference in the enzymic site of action of this amino acid in E. coli and in the rat.