A novel dipeptidyl peptidase II from the porcine ovary. Purification and characterization of a lysosomal serine protease showing enhanced specificity for prolyl bonds.

A variant form of dipeptidyl peptidase II (DPP II), initially reported under the name of "DPP V" (Eisenhauer, D. A., and McDonald, J. K. (1982) Fed. Proc. 41, 507), was detected in aqueous extracts of porcine ovaries on the basis of a markedly enhanced action on prolyl bonds. This porcine form of DPP II, which was most sensitively assayed on Phe-Pro-2-naphthylamide (Phe-Pro-NNap), was purified 1400-fold to a specific activity of 28 mumol/min/mg of protein (pH 6.0, 37 degrees C) from an aqueous extract of hog ovaries taken during pregnancy, when ovarian levels of DPP II are some 3- to 8-fold higher. Purification involved ammonium sulfate fractionation, molecular exclusion chromatography, chromatofocusing, affinity chromatography on concanavalin A-Sepharose 4B, and high performance ion exchange chromatography. The purified enzyme, which was apparently electrophoretically homogeneous at pH 3, 7, and 8.8 (pI = 5.0), was shown to be an Mr = 110,000 glycoprotein containing about 2% carbohydrate (primarily mannose) and less than 1% sialic acid, and to consist of two noncovalently linked Mr = 54,000 subunits. A serine catalytic mechanism was supported by inhibitor studies and by common mobilities seen during electrophoresis for (histochemically detected) Phe-Pro-arylamidase activity and the [14C]diisopropyl fluorophosphate-labeled enzyme. In the standard fluorometric assay at 37 degrees C, Phe-Pro-NNap (0.2 mM) was hydrolyzed optimally at pH 6.0 (Km = 45 microM; kcat = 54 s-1). In comparison to the rate seen on Lys-Ala-NNap, the usual DI P II assay substrate, rates seen on Phe-Pro-, Lys-Pro-, and Arg-Pro-NNap were about 8-, 4-, and 2-fold higher, respectively. No action occurred on N-blocked derivatives or on Pro-NNap. Action on oligopeptides appeared to be limited to tripeptides, in particular those containing proline or alanine in the P1 position, i.e. Phe-Pro-Ala (100%), Lys-Ala-Ala (35%), Ala-Ala-Ala (33%), and Gly-Pro-Ala (26%). Only a trace of activity was seen on Phe-Pro-Ala-Ala, and none on Z-Phe-Pro-Ala or Ala-Ala-Ala-OMe. Evidence for the lysosomal localization of DPP II included sedimentability and latency and its distribution, coincident with acid phosphatase, in two distinct isopycnic regions following equilibrium density centrifugation. Lysosomal heterogeneity was suggested by this dual isopycnic banding.(ABSTRACT TRUNCATED AT 400 WORDS)