DISCOVERY OF 5R-LIPOXYGENASE ACTIVITY IN OOCYTES OF THE SURF CLAM, SPISULA-SOLIDISSIMA

Arachidonic acid and 5-hydroxyeicosatetraenoic acid (5-HETE) are repor ted to induce reinitiation of meiosis in oocytes of the surf clam Spis ula sachalinensis from the Sea of Japan (Varaksin et al., Comp. Bioche m. Physiol. 101C, 627-630 (1992). As the Atlantic surf clam Spisula so lidissima is a commonly used model for the study of meiosis reinitiati on, we examined these cells for the possible occurrence of lipoxygenas es and for the bioactivity of the products. Incubation of [C-14]arachi donic acid with homogenates of S. solidissima oocytes led to the forma tion of two major metabolites: 5R-HETE, a novel lipoxygenase product, and 8R-HETE. The products were identified by HPLC, uv spectroscopy, an d GC-MS. The corresponding hydroperoxy fatty acids, the primary lipoxy genase products, were isolated from incubations of ammonium sulfate fr actionated oocyte cytosol. Arachidonic and eicosapentaenoic acids were identified as constituents of S. solidissima oocyte lipids and the fr ee acids were equally good lipoxygenase substrates. We examined the ac tivity of C18 and C20 polyunsaturated fatty acids and their lipoxygena se products on meiosis reinitiation in Spisula solidissima oocytes, us ing serotonin and ionophore A23187 as positive controls. The fatty aci ds and their derivatives were inactive. We conclude that in the surf c lam, (as in starfish), there are responding and non-responding species in regard to the maturation-inducing activity of the oocyte lipoxygen ase products, and that the lipoxygenase has another, as yet uncharacte rized, function in oocyte physiology.