HUMAN THIMET OLIGOPEPTIDASE

We have purified human thimet oligopeptidase to homogeneity from eryth rocytes, and compared it with the enzyme from rat testis and chicken l iver. An antiserum raised against rat thimet oligopeptidase also recog nized the human and chicken enzymes, suggesting that the structure of the enzyme has been strongly conserved in evolution. Consistent with t his, the properties of the human enzyme were very similar to those for the other species. Thus human thimet oligopeptidase also is a thiol-d ependent metallo-oligopeptidase with M(r) about 75000. Specificity for cleavage of a number of peptides was indistinguishable from that of t he rat enzyme, but K(i) values for the four potent reversible inhibito rs tested were lower. In discussing the results, we consider the deter minants of the complex substrate specificity of thimet oligopeptidase. We question whether substrates containing more than 17 amino acid res idues are cleaved, as has been suggested. We also point out that the f avourable location of a proline residue and a free C-terminus in the s ubstrate may be as important as the hydrophobic residues in the P2, P1 and P3' positions that have been emphasized in the past.