Abstract
Antagonism of methionine by structurally related amino acids was demonstrated in M. tuberculosis under conditions of para-aminosalicylic acid inhibition wherein an exogenous source of methionine was re-quired for restoration of growth. Methionine was antagonized by leucine, isoleucine, norleucine, norvaline, alanine, phenylalanine, tyrosine, threonine, and ornithine. Norleucine was the most effective single antagonist. The most effective antagonists were: isoleucine, norleucine, norvaline, and phenylalanine.