Investigation of the active center and catalytic mechanism of porcine kidney aminoacylase: a model of the active center.

Procine kidney aminoacylase (E.C. 3.5.1.14) is inhibited neither by phenylmethylsulfonylfluoride nor by alkylating agents (iodoacetate or iodoacetamide). Therefore reaction mechanisms including the formation of acylenzyme through seryl or cysteinyl side chains are ruled out. The enzyme is a metalloprotein that can be inactivated by ECTA and in which Co2+ is an equivalent substitute for the Zn2+ ion. The two SH groups/subunit of aminoacylase exhibit different reactivites to p-hydroxymercuribenzoate. Modification of the less reactive SH group reversibly inactivates the enzyme. We suggest that this cysteinyl side chain is situated in the active center or in its immediate vicinity. On the basis of our results we suppose a close similarity between aminoacylase and carboxypeptidase A with respect to their active center and catalytic mechanism.