THE FERTILIZING CAPACITY OF SEA URCHIN SPERM RAPIDLY DECREASES AFTER INDUCTION OF THE ACROSOME REACTION*

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Abstract
When immotile, flagella-less sperm were added to acid-dejellied eggs of Strongylocentrotus purpuratus, 11% of the eggs fertilized. Addition of soluble egg jelly increased the percentage fertilization to 90.5. Over 50% of the sperm exposed to egg jelly underwent the acrosome reaction compared to only 3-5% in the absence of jelly. Egg jelly was added to flagella-less sperm to induce the acrosome reaction and dejellied eggs added at various times. The fertilizing capacity of the sperm decreased with first order kinetics with 50% loss by 23 s after induction of the acrosome reaction. Intact, motile sperm bind to formaldehyde-fixed eggs with maximum binding occurring 40 s after sperm addition. After 40 s the sperm begin to detach from the fixed eggs and by 240 s none remain attached. Sperm detachment from fixed eggs and loss of fertilizing capacity after the acrosome reaction show a close temporal correlation.