Utilization of d-phenylglycyl-glycine in Escherichia coli

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Abstract
Escherichia coli K 12 is able to utilize the dipeptide d-phenylglycyl-glycine as a source of glycine. Growth experiments with a glycine auxotrophic mutant show that utilization of the dipeptide is competitively inhibited by d-alanine at a K iof 4×10-4 M. In contrast, l-alanyl-l-alanine which is transported via the system specific for dipeptides does not interfere with the utilization of d-phenylglycyl-glycine. This indicates that the dipeptide is hydrolyzed prior to uptake, and d-alanine therefore competes with the uptake of glycine via the transport system common for both amino acids. This was confirmed by examining the growth response of various transport mutants. A mutant deficient in the transport of oligo- and dipeptides grows as well as the wild type on d-phenylglycyl-glycine, whereas the growth of mutants deficient in the transport of glycine is severely impaired or prevented with this dipeptide. It is therefore demonstrated that d-phenylglycyl-glycine is hydrolyzed prior to uptake. This is a mechanism of peptide utilization in E. coli K 12 which is distinct from that described so far for other dipeptides.