Chemistry and biology of nitrosated peptides

All peptides undergo nitrosation at the terminal primary amino group to generate a diazopeptide and at the peptide N-atoms to produce an N-nitrosopeptide. With acidified nitrite, diazopeptides usually form more readily than N-nitrosopeptides, but quickly decompose. Diazopeptides form rapidly at neutral pH from gaseous nitrogen oxides and are relatively stable under these conditions. N-nitrosopeptides are more stable than diazopeptides at both acidic and neutral pH. Because of their availability as substrates, peptides are probably involved in endogenous nitrosation associated with the diet and from the inhalation of nitrogen oxides as in tobacco smoking. Both diazopeptides and N-nitrosopeptides are cytotoxic, but a causal role for these compounds in human cancer has yet to be demonstrated.