Amino-acid utilization in bacterial growth. 1. Peptide utilization by a leucine-requiring mutant of Escherichia coli

Abstract
The growth of a leucine-requiring mutant of E. coli is inhibited by L-isoleucine, L-valine, DL-methionine and DL-norleucine. D-Valine and D-isoleucine are not inhibitory. The inhibition by L-isoleucine is competitive. The inhibition by L-isoleucine and L-valine is antagonized non-competitively by either L-leucylglycine or glycyl-L-leucine. Explanations of the results are considered. The presence of hydrolytic peptidases is not incompatible with non-hydrolytic peptide utilization, for example, by transpeptida-tion reactions.