Nitration of Pepsin, Thrombin and Carboxypeptidase B with Tetranitromethane

Tetranitromethane has been employed to examine the role of tyrosyl residues in the mechanism of action of a series of enzymes. Nitration partially inactivates pepsin but loss of peptidase and protease activities occur at different rates. The clotting activity of thrombin is virtually abolished by nitration with only a slight decrease in esterase activity. Both the esterase and peptidase activity of carboxypeptidase B are abolished simultaneously with the modification of one tyrosyl residue, indicating the marked similarity between this enzyme and carboxypeptidase A. Trypsin and chymotrypsin are almost unaffected by tetranitromethane. The role of tyrosyl residues in these enzymes is discussed.