MAGNESIUM REQUIREMENT IN FERTILIZATION PROCESS OF SEA URCHINS.

The Mg requirement in fertilization was investigated in sea urchins. It was found that when sea urchin eggs were inseminated in sea water free of Mg , little fertilization took place. Even when spermatozoa pre-treated with dissolved egg-jelly to induce the acrosome reaction, which needs Ca , were used, the fertilization rate remained quite low in the absence of Mg . In Strongylo-centrotus intermedius, the lowest concentration of Mg required for 50% fertilization was 0.05 mM in the presence of 10 mM Ca , whereas that of calcium was 3 mM in the presence of 49 mM Mg . These critical concentrations increased when the concentration of the other ion decreased. Removal of Mg or Ca or both from the suspending medium had little adverse effect on sperm motility. The elevation of the fertilization membrane was also induced by butyric acid independent of the presence or absence of Mg and/or Ca . These results indicate that Mg are required at least in some process(es) between acrosome reaction and fertilization membrane elevation, such as sperm penetration or membrane fusion.