Proteins and amino acids as scavengers of nitrite: inhibitory effect on the formation of nitrosodimethylamine and diazoquinone.

Protein and its components in high concentrations similar to those found in the digestive tract effectively scavenged nitrite and thus inhibited the formation of mutagens from nitrite. Various amino acids at 100 mM, bovine serum albumin (BSA) and trypsinized casein at 100 mg/ml effectively decreased the nitrite level of 50 mM-nitrite solution at pH 3 and 37 degrees C. Most, but not all, amino acids can convert nitrite into nitrogen gas; Pro can be converted into non-mutagenic nitrosoproline, CySH to S-nitrosocysteine, Trp to weakly mutagenic nitrosotryptophan and Tyr to non-mutagenic diazotyrosine. BSA was cross-linked, probably owing to the reaction of Tyr and Lys residues. Most amino acids inhibited more than 50% of nitrosodimethylamine formation in the reaction between 200 mM-dimethylamine and 50 mM-nitrite at pH 3 and 37 degrees C; BSA inhibited 50% of nitrosodimethylamine formation, and trypsinized casein, 100%. Most amino acids inhibited more than 50% of p-diazoquinone formation in the reaction between 25 mM-phenol and 100 mM-nitrite at pH 3 and 37 degrees C; BSA inhibited 80%, and trypsinized casein, 95% of such formation. Trypsinized casein effectively inhibited the development of the mutagenic effects attributable to the formation of diazobamethan from bamethan and nitrite.