Effects of pH on carboxypeptidase‐Y‐catalyzed hydrolysis and aminolysis reactions

Abstract

The pH dependencies of serine carboxypeptidase‐Y‐catalysed hydrolysis and aminolysis reactions using L‐amino acids and L‐amino acid amides as nucleophiles, have been studied and analyzed. The results reveal two catalytically important ionizing groups of the enzyme with rather similar pK values (5–6), the active site His397 and a possibly Glu residue, which is not only important in interactions with carboxylic groups of substrates and nucleophiles [Liao, D.‐I., Breddam, K., Sweet, R. M., Bullock, T. & Remmington, S. J. (1992) Biochemistry 31, 9796–9812], but also indirectly play a role in catalysis. This explains the pH behaviour of hydrolysis of both peptide and ester substrates and further, that L‐amino acid amides are better nucleophiles in aminolysis reactions than L‐amino acids. Copyright © 1994, Wiley Blackwell. All rights reserved