Acrosome Reaction‐Inducing Substance Purified from the Egg Jelly Inhibits the Jelly‐Induced Acrosome Reaction in Starfish: An Apparent Contradiction

Previous studies indicated that two components of the egg jelly are required for induction of the acrosome reaction in starfish: a sulfated glycoprotein called acrosome reaction‐inducing substance (ARIS) and a diffusible organic substance(s) called Co‐ARIS. In the present study the sites of action of ARIS and Co‐ARIS and their temporal relationships were examined. When sperm had been treated for a few minutes with ARIS, or a crude preparation of Co‐ARIS (Fraction M8), or inadequate amounts of jelly, or sufficient jelly in low Ca2+ sea water, they did not undergo the acrosome reaction when the deficiencies were corrected. Moreover, they became nonresponsive to the jelly. Pronase digest of ARIS (P‐ARIS) but not of Fraction M8 retained this capacity. A steroidal saponin purified as Co‐ARIS did not have this capacity. This suggests the presence of a third jelly component, probably an oligopeptide(s), participating in induction of the acrosome reaction. Activation of Ca2+ ‐uptake seems to be at least one, if not the only, action site of ARIS and Co‐ARIS, because ARIS, P‐ARIS, and Fraction M8 inhibited jelly‐induced Ca2+ ‐uptake by sperm, and because the calcium ionophore A23187 by‐passed the blockage by these components of the jelly‐induced acrosome reaction.