Biochemical and immunological characterization of the acrosome reaction-inducing substance (ARIS) of hFF.

Gel filtration experiments with 3H-progesterone labeled hFF demonstrated that the AR-inducing activity of hFF might be mediated by a progesterone-binding protein. Further immunological investigations added evidence in support to ARIS being identical with the SERPIN CBG. Moreover, only the protein-progesterone-complex was able to induce AR. It is suggested that the CBG-progesterone-complex is proteolytically cleaved at the plasma membrane of spermatozoa, releasing a high local concentration of progesterone which leads to induction of the AR.