Copper ions and hydrogen peroxide form hypochlorite from NaCl thereby mimicking myeloperoxidase

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Abstract
Sea urchins have elaborated multiple defenses to assure monospermic fertilization. In this work, we have concentrated on a study of the mechanism(s) by which hydrogen peroxide (H2O2) prevents polyspermy in Arbacia punctulata. We found that it is not H2O2 but probably hypochlorous acid/hypochlorite (HOCl/OCl−) derived from H2O2 that is toxic to the supernumerary sperm. The spermicidal activity of H2O2 is potentiated by at least one order of magnitude by cupric ions (Cu2+). This increased toxicity is not due to the formation of hydroxyl radicals (·OH) because ·OH scavengers did not counteract the activity of Cu2+. More-over, substitution of Cu2+ by ferrous ions (Fe2+), which are known to cause formation of ·OH from H2O2, had no effect on fertilization even at 102−103 times higher concentrations. In contrast, 3-amino-1,2,4-triazole (AT), an HOCl/OCl− scavenger, totally reversed the toxic effects of Cu2+. Furthermore, we found that HOCl/OCl− is generated in solutions of H2O2 and Cu2+ in the presence of 0.5 M NaCl and that its accumulation is abolished by AT. Thus it is possible that the antifertility properties of copper are due to its ability to mediate formation of HOCl/OCl−. HOCl/OCl− generated by Cu2+ from H2O2 and Cl−, a low concentration of exogenously added HOCl/OCl−, or increased concentrations of H2O2 has similar inhibitory effects on the fertilization process in sea urchins. Therefore, we suggest that polyspermy is prevented by the action of a myeloperoxidase that affects the formation of HOCl/OCl− from the Cl− present in sea water through reaction with H2O2 generated by the newly fertilized egg.