Chemical modification of tyrosine residues in glyoxalase I from yeast and human erythrocytes

1. Yeast glyoxalase I was inactivated by N-acetylimidazole and tetranitromethane, the latter process following pK app 7.31 and irreversibly producing a protein with a spectrum typical of 3-nitrotyrosine. 2. For yeast glyoxalase I, amino-acid analysis and protection studies with S-(p-bromobenzyl)glutathione, a competitive inhibitor, indicated two classes of tetranitromethane-reactive tyrosine residues, fast- and slow-reacting, with the latter class containing the crucial tyrosine(s). 3. Human erythrocyte glyoxalase I was inactivated by tetranitromethane in fast and slow processes, protection studies in this case indicating the important tyrosine(s) as fast-reacting.