Nitrite converts 2-amino-alpha-carboline, an indirect mutagen, into 2-hydroxy-alpha-carboline, a non-mutagen, and 2-hydroxy-3-nitroso-alpha-carboline, a direct mutagen.

2-Amino-alpha-carboline [26148-68-5] which was isolated from a pyrolysate of soybean globulin and which was mutagenic to Salmonella typhimurium in the presence of a rat-liver microsomal fraction (S9 mix), was converted into non-mutagenic 2-hydroxy-alpha-carboline by treatment with nitrite in acidic conditions. However, on prolonged treatment with nitrite and acid, 2-hydroxy-alpha-carboline was further converted into a new mutagen which did not require S9 mix for exhibition of the mutagenicity. This direct-acting mutagen was found to be 2-hydroxy-3-nitroso-alpha-carboline by mass and proton magnetic resonance spectroscopies.