NOVEL SH-TYPE CARBOXYPEPTIDASE IN THE INNER MEMBRANE OF RAT-LIVER MITOCHONDRIA

A carboxypeptidase from rat liver mitochondria was partially purified by discontinuous sucrose gradient centrifugation, washes with NaCl/KBr/Tris buffer, and solubilization with 2 M NaCl in the presence of soybean trypsin inhibitor bound to CM‐cellulose. By means of dodecylsulfate/polyacrylamide gel electrophoresis a molecular weight of 34500 was determined; a value of 38000 was estimated by Sephadex G‐100 gel filtration. The carboxypeptidase was completely inhibited by 3 mM Hg2+. In the presence of 3 mM Cu2+ 50% of the catalytic activity was inhibited. Among several peptides tested Cbz‐Ala‐Phe, Cbz‐Leu‐Phe, Cbz‐Phe‐Leu, and Cbz‐Phe‐Phe, were good substrates. The enzyme activity exhibited a pH optimum of around 9 with Cbz‐Ala‐Phe as a substrate. After submitochondrial fractionation it was found that the carboxypeptidase is located in the inner mitochondrial membrane. Copyright © 1979, Wiley Blackwell. All rights reserved