Oxidation of n-formyl methionyl chemotactic peptide by human neutrophils

Human neutrophils during phagocytosis oxidized the synthetic chemotactic peptide, n-formyl methionyl-leucyl-phenylalanine (n-FMLP), to its sulfoxide derivative (n-FMsLP). The oxidation of n-FMLP by phagocytosing neutrophils was inhibited by methionine, but not by methionine sulfoxide, leucine, or phenylalanine, confirming that it was the methionine moiety of n-FMLP that was oxidized. The oxidation of n-FMLP was also inhibited by myeloperoxidase inhibitors or catalase, but not by SOD or mannitol, suggesting the involvement of the myeloperoxidase system. Since n-FMsLP does not have chemotactic activity, the oxidation of n-FMLP by phagocytosing neutrophils may be one mechanism by which neutrophils modulate the inflammatory process.