POTENTIAL INVOLVEMENT OF KALLIKREIN HK2 IN THE HYDROLYSIS OF THE HUMAN SEMINAL-VESICLE PROTEINS AFTER EJACULATION

We have recently demonstrated in liquefied human seminal plasma the pr esence of the novel kallikrein hK2 in association with protein C inhib itor (PCI) as a 75-kDa complex. In the present study, we showed that h K2, immediately after ejaculation, was recovered only in its free form but complex formation with PCI occurred rapidly thereafter and was co mpleted within 10 minutes. That reaction required an enzymatically act ive kallikrein. In order to determine the patterns of hydrolysis of ma jor seminal vesicle proteins, semenogelins and fibronectin were expose d to hK2 and to hK3 (prostate-specific antigen or PSA) and cleavage se quences were identified by N-terminal sequencing. Free hK2 was able to hydrolyze semenogelins and fibronectin in vitro. Most of cleavage sit es were at the carboxyl-side of arginyl residues. Semenogelins were hy drolyzed to a similar extent by catalytic (and similar) concentration of either hK2 or PSA though no common cleavage sites was identified fo r both proteinases. Unlike semenogelins, fibronectin was hydrolyzed mu ch more efficiently by hK2: than by PSA. These results show that hK2 i s enzymatically active during a short period of time after ejaculation , that major seminal vesicle proteins can be the target of this proteo lytic activity, and that hK2 and PSA have different substrate specific ities.