Partial purification and characterization of an ovarian tripeptidyl peptidase: a lysosomal exopeptidase that sequentially releases collagen-related (Gly-Pro-X) triplets.

The pregnant hog ovary is a rich source of a novel exopeptidase that catalyzes the release, at pH 5.0, of collagen-related (P3-P2-P1) "triplets" such as Gly-Pro-Met, Gly-Pro-Arg, and Gly-Pro-Ala from arylamide derivatives, provided the N termini are unsubstituted. Corresponding derivatives of related (P2-P1) dipeptides (Pro-Met, Pro-Ala) or (P1) amino acids (Met, Arg, Ala) are not attacked. The enzyme was purified 58-fold from a detergent extract of a water-extracted tissue residue. Activity was determined on Gly-Pro-Met-2-naphthylamide at pH 4.5 and 37 degrees C (Km 0.45 mM; Vmax 722 nmoles/min/mg protein). The responsible Mr 55,000 exopeptidase, termed "tripeptidyl peptidase", forms high-Mr aggregates, belongs to the serine catalytic class, and has a lysosomal localization. Gly-Pro-Ala triplets were released sequentially at pH 5.0 from a Mr 14,000 polypeptide, poly(Gly-Pro-Ala-). When this reaction was coupled to that of homologous dipeptidyl peptidase II, the liberated tripeptides were reduced to dipeptides and free amino acids: (Gly-Pro-Ala)n----nGly-Pro-Ala----nGly-Pro + nAla.