title: Evidence for the involvement of metalloendoproteases in the acrosome reaction in sea urchin sperm.
abstract: An essential initial step in fertilization in the sea urchin Strongylocentrotus purpuratus is an intracellular membrane fusion event in the sperm known as the acrosome reaction. This Ca2+-dependent, exocytotic process involves fusion of the membrane of the acrosomal vesicle and the plasma membrane. Recently, metalloendoproteases requiring divalent metals have been implicated in several Ca2+-dependent membrane fusion events in other biological systems. In view of the suggested involvement of Zn2+ in the sea urchin sperm acrosome reaction (Clapper, D.L., Davis, J.A., Lamothe, P.J., Patton, C., and Epel, D. (1985) J. Cell Biol. 100, 1817-1824) and the fact that Zn2+ is a metal cofactor for metalloendoproteases, we investigated the potential role of this protease in the acrosome reaction. A soluble metalloendoprotease was demonstrated and characterized in sperm homogenates using the fluorogenic protease substrate succinyl-alanine-alanine-phenylalanine-4-aminomethylcoumarin. The protease was inhibited by the metal chelators EDTA and 1,10-phenanthroline, and activity of the inactive apoenzyme could be reconstituted with Zn2+. The metalloendoprotease substrate and inhibitors blocked the acrosome reaction induced either by egg jelly coat or by ionophore, but had no effect on the influx of Ca2+. These observations suggest that inhibition occurs at a step independent of Ca2+ entry. Overall, the results of this study provide strong indirect evidence that the acrosome reaction requires the action of metalloendoprotease.
mesh_terms: D000177:Acrosome / Q000201:enzymology*; D000818:Animals; D010450:Endopeptidases / Q000378:metabolism*; D005306:Fertilization; D005343:Fibrinolytic Agents / Q000378:metabolism; D007700:Kinetics; D008297:Male; D008666:Metalloendopeptidases; D008667:Metalloproteins / Q000378:metabolism; D012617:Sea Urchins; D013094:Spermatozoa / Q000201:enzymology* / Q000502:physiology*
chemical_list: D005343:Fibrinolytic Agents; D008667:Metalloproteins; D010450:Endopeptidases; D008666:Metalloendopeptidases