Gelatin zymograms of bFF and bS showed GA110 and 62 kDa gelatinses in adsition to several minor ones. Of these, GA110 gelatinase was abolished by treating bFF or bS with bOF and interestingly, its enzymatic activity was enhanced by adding EDTA to bFF or bS before zymographic analyses. Experiments using specific inhibitors of MMPs indicated that GA110 and 62 kDa proteins were indeed gelatinases. Immunoblotting experiments using an antibody against human MMP-2 showed that both GA110 and 62 kDa were an MMP-2 isoform and active MMP-2, respectively. The results suggest that the interaction between bFF and bOF can occur at the time of fertilization.