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Different roles of Zn ions during sperm–ova interactions. Zona pellucida (ZP) hardening occurs through membrane protein changes when the ZP protein acts using the Zn-binding protease. The major functions of zinc in the prevention of polyspermy are depicted in the figure. 1—Zn dependent metalloprotease on zona pellucida for sperm recognition; 2—how Zn efflux results in polyspermy.
