Carboxypeptidase activity was detected in swine kidney microsomes. The enzyme was solubilised by treatment with trypsin and toluene. Approximately 330-fold purification was achieved by subsequent chromatography on DEAE-cellulose and hydroxylapatite.
As shown by polyacrylamide gel investigation, the carboxypeptidase preparation thus obtained was practically pure. It still contains trace impurities of aminopeptidase M which is quite similar in physical properties. The molecular weight of the carboxypeptidase was 240000 as determined by Sephadex gel filtration. It is activated by manganese ions and exhibits a pH-optimum at 7.75.
The carboxypeptidase preferentially attacks substrates with a prolyl residue in the last but one position. No chain length dependence was found. Peptides free of proline were also cleaved, but normally at a rather low rate. The designation carboxypeptidase P (indicating its preference of proline peptide bonds) is therefore suggested.
The physiological role of the new peptidase is discussed.