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Stereospecificity of Tripeptide Utilization in a Methionine Auxotroph of Escherichia coli K-12

Department of Microbiology, University of Tennessee, Knoxville, Tennessee 37916 and Chemistry Department, Richmond College of City University of New York, New York 10301

ABSTRACT

The stereospecificity of peptide utilization in Escherichia coli K-12 4212, a methionine auxotroph, was investigated using diastereomers of trimethionine and trimethionine methyl ester. Of the eight stereoisomers examined, only L-Met-L-Met-L-Met, L-Met-L-Met-D-Met, and D-Met-L-Met-L-Met and the corresponding methyl esters serve as growth substrates. Triornithine-resistant mutants of strain 4212 were isolated which failed to transport D-Met-L-Met-L-Met. These results provide evidence that an oligopeptide containing a D residue at its amine terminus can enter E. coli by the oligopeptide transport system.