IDENTIFICATION, PURIFICATION AND PARTIAL CHARACTERIZATION OF A CARBOXYPEPTIDASE FROM THE MATRIX OF RAT-LIVER MITOCHONDRIA - A NOVEL METALLOENZYME

A novel carboxypeptidase has been purified to apparent homogeneity from the matrix fraction of rat liver mitochondria by using a procedure mainly based on immobilized-metal-affinity chromatography (IMAC). This carboxypeptidase has been named mCP-III, since it represents the third major peak of carboxypeptidase activity after the IMAC step of purification. mCP-III hydrolyses a number of N-blocked dipeptides, with preference for Cbz-Phe-Ala, and shows no degrading activity towards I-125-casein. The optimal pH of its activity is 7.6, the apparent K-m for Cbz-Phe-Ala is 0.12 mM and the specific activity is 145.5 mu mol/min per mg of protein. The enzyme is a typical metalloproteinase, is inhibited by 1,10-phenanthroline and carboxypeptidase inhibitor and re-activated by added Zn2+ and Co2+. The molecular mass estimated by molecular-sieve h.p.l.c. was approx. 115 kDa with two protein bands of 61 and 50 kDa shown by SDS/PAGE analysis, indicating that the enzyme is active as a dimer. This is the first clearly identified carboxy-peptidase within mitochondria.