Identification and partial characterization of a metallopeptidase from porcine ovaries

Presence of angiotensin-converting enzyme in follicular fluids of porcine ovaries and its possible involvement in the intrafollicular breakdown of bradykinin

The follicular fluid of porcine ovaries contains a metalloenzyme capable of hydrolyzing the synthetic substrate, benzyloxycarbonyl-Val-Lys-Met-MCA. This enzyme was purified by ammonium sulfate fractionation followed by column chromatography on DEAE-cellulose, CM-cellulose, Zn(2+)-chelating Cellulofine, and Diol-300 gel-filtration columns. The molecular weight of the purified enzyme was estimated to be 170,000 by SDS-PAGE and 400,000 by gel-filtration analysis, suggesting that the native enzyme is a dimer of the 170-kDa subunit polypeptide. The enzyme activity was drastically enhanced by the presence of chloride ion, and strongly inhibited by captopril and bradykinin potentiator B. A 9-residue peptide containing a processing site of human amyloid precursor protein was degraded by its dipeptidyl carboxypeptidase activity. Furthermore, the purified protein was recognized by specific antibody raised against human angiotensin-converting enzyme. The enzyme rapidly degraded bradykinin in vitro. These results indicate that benzyloxycarbonyl-Val-Lys-Met-MCA-hydrolyzing enzyme is a porcine angiotensin-converting enzyme, and that the enzyme may play a role in bradykinin turnover within the follicles of porcine ovaries.

Identification of porcine follipsin as plasma kallikrein, and its possible involvement in the production of bradykinin within the follicles of porcine ovaries

To determine the identity of porcine follipsin, a plasma kallikrein cDNA clone was isolated from a porcine liver cDNA library. The clone encoded a protein of 643 amino acids, exhibiting identities 79.7, 72. 9, and 74.4% homologous to human, rat, and mouse plasma prekallikrein, respectively. The amino acid sequences of four internal peptides isolated from the tryptic digest of follipsin were all found in the deduced sequence. Authentic plasma kallikrein was purified from porcine plasma and compared directly with follipsin. Actions on synthetic substrates and behaviors with proteinase inhibitors were indistinguishable between these two enzymes. The cDNA was expressed in COS-7 cells and the recombinant protein was prepared from the culture medium of these cells. No active enzyme could be obtained, but the expressed protein was reacted with anti-porcine plasma kallikrein antibody. The mRNA was detected only in the liver in northern blot analysis. RT-PCR analysis of RNAs revealed that porcine testis, in addition to the liver, expressed the corresponding mRNA. In the ovary, plasma kallikrein was detected as a main band of the active form (Mr = 85,000) and the band of the minor inactive precursor form (Mr = 80,000), respectively. In contrast, the liver extract contained only the precursor form. Incubation of high molecular weight kininogen with follicular fluid plasma kallikrein resulted in an increased production of bradykinin. Further, the fresh fluid of large-sized follicles of porcine ovaries was found to contain this peptide hormone at a detectable level. These results indicate that porcine follipsin is plasma kallikrein, and that the enzyme may be involved in the production of bradykinin within ovarian follicles.