Selective free radical reactions with proteins and enzymes. Reactions of inorganic radical anions with trypsin

Abstract

The selective reactivity of the radical anions (CNS)^– ₂, Br^– ₂ and I^– ₂, with amino-acids has been used to identify residues essential to the activity of bovine pancreatic trypsin. A combination of pulse radiolysis and inactivation measurements shows that histidine damage leads to inactivation between pH 4 and 10.5. Reaction with tryptophan and tyrosine residues also occurs over this pH range, but leads to inactivation only at pH > 9. This latter process involves an irreversible configurational change. In trypsin, the tyrosine residues are more reactive with the radical anions than they are in some other enzymes.