Metabolism of phenylalanine-containing peptide amides in Escherichia coli.

Simmonds, Sofia (Yale University, New Haven, Conn.) and David D. Griffith. Metabolism of phenylalanine-containing peptide amides in Escherichia coli. J. Bacteriol. 83:256-263. 1962.-A study was made of the hydrolysis, by fresh and lyophilized cells of a phenylalanine auxotroph of Escherichia coli, of l-phenylalanyl-glycinamide and glycyl-l-phenylalaninamide. The former dipeptide amide is hydrolyzed to yield phenylalanine and glycinamide, the latter to yield glycine and phenylalaninamide. The slow degradation of phenylalaninamide yields the free amino acid. In spite of the presence of intracellular activity toward the two dipeptide amides, neither permits as much growth as that observed with an equimolar concentration of free phenylalanine. The relatively small extent of growth on the dipeptide amides, and also on l-phenylalaninamide, appears to result from the inability of the cells in a growing culture to take up all of the exogenous amide added to the growth medium. This, in turn, probably reflects the presence in the medium of the amides as a mixture of charged and uncharged forms, of which only the latter are readily taken into the cells.