Tetranitromethane as a Nitrating Reagent for Tyrosine and Tyrosine-Containing Peptides and Proteins

After nitration of hemoglobin and ribonuclease with tetranitromethane, the sum of tyrosine and nitrotyrosine accounted for 80% or less of the tyrosyl residues known to be present in these proteins. Reasons for this discrepancy were explored by nitrating tyrosine, glycyltyrosine, and glycyltyrosylglycine. Ninhydrin-negative substances containing the carbon atoms of tyrosine were isolated in addition to nitrated tyrosines, which may account for the apparent loss of tyrosine in nitrated proteins.