Inhibition of sea urchin sperm acrosome reaction by antibodies directed against two sperm membrane proteins. Characterization and mechanism of action.

The egg jelly-induced acrosome reaction is inhibited by polyclonal antibodies raised against either of two S. purpuratus sperm-membrane proteins, of Mr 80 and 210 kD. Although the two antigens used have dissimilar CNBr peptide maps, antisera produced against each of them cross-react with both proteins. Inhibition of the egg jelly-induced acrosome reaction by the antisera is bypassed by a combination of the ionophores monensin and A23187. This result, along with data showing that the antisera inhibit egg jelly-induced uptake of 45Ca2+, suggests that the antisera may block both Ca2+ uptake and Na+/H+ exchange in the sperm. The acrosome reaction blockage appears to be caused by the same component of the polyclonal sera responsible for cross-reaction; consequently, these antisera cannot be used to determine whether one or both of the cross-reacting proteins modulate a critical step in the acrosome reaction.