[Molecular dynamics of human intrafollicular plasma kallikrein and the mechanism of activation of tissue-type plasminogen activator (tPA) in ovarian follicles].

Tissue-type plasminogen activator (tPA)/plasmin system is generally believed to play an important role in follicle wall degradation upon ovulation. For examination of the proteolytic activation of tPA within the follicle, human plasma kallikrein (hPK) was purified from preovulatory follicular fluid obtained from women hyperstimulated by GnRHa-hMG-hCG in in vitro fertilization procedures. After ammonium sulfate fractionation, three enzyme fractions were isolated in the DEAE-cellulose ionic exchange column chromatography. Each fraction was further purified by various column chromatographies using CM-cellulose, benzamidine-Sepharose 6B, heparin-Cellulofine, and Sephacryl S-300. Enzymatic (substrate specificity, susceptibility to various proteinase inhibitors), electrophoretic, and immunological characterization of the enzymes revealed that they were hPK in free form (Mr = 89,000-90,000), in complex with alpha 2-macroglobulin (Mr = 730,000), and a newly-found isoform of pPK (Mr = 80,000-87,000). Each fraction was capable to convert human single-chain tPA (sctPA) to its active two-chain form. The present data also demonstrates that the activation of tPA by the alpha 2-macroglobulin fraction is due to the action of a bound proteinase distinct from hPK, indicating the presence of an additional tPA activator. These proteinases are presumably involved in triggering of the tPA/plasmin system by activating tPA upon ovulation.