Sperm Penetration of the Vitelline Envelope of Sicyonia ingentis Eggs is Mediated by a Trypsin‐like Lysin of Acrosomal Vesicle Origin

The sperm of the decapod crustacean Sicyonia ingentis are nonmotile, unistellate cells. At spawning, mated females release both stored sperm and eggs. The sperm bind, via the tip of their anterior appendage, to the egg's vitelline envelope (VE), rapidly undergo acrosomal exocytosis, and penetrate the VE. In the present study we used protease inhibitors to show that sperm penetration of the VE is due to the activity of a sperm trypsin-like protease(s). Sperm extracts contained several proteases when examined using gelatin-substrate SDS-PAGE, with two major bands of relative molecular weight 46 kD and 30 kD. Using fluorescent peptidyl-MCA substrates, sperm extract showed trypsin-like and aminopeptidase-like activities, but no chymotrypsin-like activity. Sperm extracts were found to degrade isolated VEs. Using soybean trypsin inhibitor and anti-inhibitor antibodies, protease was localized at the light and electron microscope levels to the acrosome remnants of reacted sperm.