FURTHER INDICATIONS OF THE MULTICOMPONENT NATURE OF THE ACROSOME REACTION-INDUCING SUBSTANCE OF HUMAN FOLLICULAR-FLUID

Human follicular fluid (hFF), which has been treated with either unspe cific proteases or dextran-coated charcoal (DCC) to remove proteins an d/or steroids, cannot successfully induce the acrosome reaction (AR). After the removal of steroids, AR-inducing activity can be restored to hFF by supplementation with exogenous progesterone, but only in the p resence of intact protein. Gel filtration experiments with H-3-progest erone-labelled hFF showed elution of the radioactive signal in the hig h molecular weight range, corresponding to bound progesterone. AR-indu cing activity was seen in exactly the same fraction. Based on these re sults, the acrosome reaction-inducing substance (ARIS) appears to be a complex of progesterone and a progesterone-binding protein, which was shown to be identical with the plasma protein corticosteroid-binding globulin (CBG) by immunological techniques. AR induction was only obse rved in the presence of both CBG and progesterone, suggesting a combin ed effect of the two components, (C) 1995 Wiley-Liss, Inc.