The Inactivation of Pepsin by Diazoacetylnorleucine Methyl Ester

Abstract Diazoacetyl-dl-norleucine methyl ester rapidly inactivates pepsin. In the presence of cupric ions, only 1 eq of norleucine is introduced per molecule of pepsin. In the absence of cupric ions, the reaction is much slower, inactivation is not complete, and more than 1 eq of norleucine is incorporated. Little or no reaction occurs with pepsinogen or with pepsin previously inactivated by exposure to pH 8. The norleucine introduced into pepsin can be removed by treatment with hydroxylamine. Thus, there is reason to conclude that a single carboxyl group at the active site of pepsin may have been esterified by this reagent.