SPECIFICITY IN THE INDUCTION OF POLYSPERMY IN SEA URCHIN EGGS BY SOYBEAN TRYPSIN INHIBITOR

Sea urchin egg cortical granules contain a Soybean trypsin inhibitor (SBTI)-sensitive protease that is activated and secreted upon fertilization. Results obtained in several laboratories have implicated this activity in the cortical reaction, elevation of the fertilization envelope, and the establishment of the block to polyspermy. These conclusions are supported in part by studies using a variety of trypsin inhibitors. This interpretation has recently been challenged, however, and past results with soybean trypsin inhibitor (SBTI) and other agents were attributed to a non-specific protein effect (Dunham et al., 1982). We have re-examined this question by studying the effects of native and inactivated SBTI on purified egg protease and the promotion of polyspermy. Protease was purified from unfertilized eggs by SBTI-affinity chromatography in the presence of benzamidine-HCl to minimize autodegradation. Inactivation of SBTI by acid or alkali treatment greatly diminished its ability to inhibit the egg protease or to cause polyspermy. We also observed a correlation between the relative potencies of five senne protease inhibitors and their ability to promote polyspermy. We conclude that induction of polyspermy by SBTI and other protease inhibitors is indeed due to inhibition of the egg protease.