Oligopeptide transport in Escherichia coli. Specificity with respect to side chain and distinction from dipeptide transport.

A lysine auxotroph of Escherichia coli W can use lysine oligopeptides as a source of the required amino acid. A mutant, defective in oligopeptide transport, was isolated from this strain with the use of resistance to the bactericidal action of triornithine as a selection procedure. The triornithine-resistant mutant could no longer grow upon lysine oligopeptides. In an analogous manner a triornithine-resistant mutant of a glycine auxotroph lost the ability to grow upon glycine oligopeptides. It is concluded that lysine, ornithine, and glycine oligopeptides use a common transport system, which is lost in the triornithine-resistant strain. This conclusion is substantiated by studies that show competition among these oligopeptides for entry into the cell. Tyrosine oligopeptides can also compete, and they are presumed to use the same transport system. This lack of specificity with respect to side chain is taken as an indication that a single system may be used for oligopeptide transport and therefore is in marked contrast to the transport of the free amino acids, for which several distinct systems are required. It is shown that dipeptides use predominantly a separate system, although they possess limited ability to enter by the oligopeptide mechanism. In contrast, oligopeptides cannot be transported by the specific dipeptide system or systems.