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

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Abstract
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 orgnaic 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.