Pig platelet acidic carboxypeptidases.

Abstract

Pig platelet acidic carboxypeptidases hydrolyzed only N-blocked dipeptides with bulky aromatic and aliphatic hydrophobic amino acids. The optimum hydrolysis of these substrates was at pH 5.0. The main acidic carboxypeptidase in pig platelet lysate was lysosomal carboxypeptidase A (1CPA), which hydrolyzed Cbz-Phe-Ala at the highest rate. A lower activity of this enzyme was found on Cbz-Glu-Tyr and Cbz-Glu-Phe. 1CPA also hydrolyzed Cbz-Glu-Tyr at pH 3.5. No activity of lysosomal carboxypeptidase B in platelet lysate was detectable using Bz-Gly-Arg. Pig platelet acidic carboxypeptidase hydrolyzed Cbz-Pro-Phe and Cbz-Pro-Ala, which are specific substrates of lysosomal prolylcarboxypeptidase, more slowly. The incubation of platelet lysate with plasma did not influence the rate of hydrolysis of Cbz-Glu-Tyr, whereas no hydrolysis of Cbz-Pro-Phe was observed.