Transport and metabolism of bacilysin and other peptides by suspensions of Staphylococcus aureus.

L-Alanyl-L-tyrosine and glycyl-L-phenylalanine labelled with 14C competed with each other and with the dipeptide antibiotic bacilysin for transport into Staphylococcus aureus NCTC 6571 in a medium which did not support growth. They also competed with other dipeptides and several tripeptides. The fast initial transport ofthe two labelled peptides appeared to show Michaelis-Menten kinetics. Neither was transported into a bacilysin-resistant mutant of S. aureus NCTC 6571, although tyrosine was taken up by the mutant as readily as it was by the parent strain. Uptake of alanyltyrosine or glycylphenylalanine was followed by rapid hydrolysis of the peptide and the excretion of tyrosine or phenylalanine. Glycine liberated from glycylphenylalanine was partly degraded and partly incorporated into the bacterial wall. The behaviour of these dipeptides paralleled the inactivation of bacilysin by suspensions of S. aureus and the appearance of its C-terminal amino acid, anticapsin, in the extracellular fluid.