Discovery of an 11 (R)- and 12(S)-lipoxygenase activity in ovaries of the mussel Mytilus edulis.

Eicosanoid biosynthesis was investigated in mussel gonads by incubation of tissue homogenates with radiolabeled arachidonic acid and analysis of the products by radio-high-performance liquid chromatography. No radiolabeled metabolites were formed in homogenates of testes, but two major metabolites were synthesized by ovarian preparations. The radiolabeled metabolites were analyzed by mass spectrometry and chiral chromatography and identified as 11 (R)-hydroxy-5,8,1 2,14-eicosatetraenoic acid and 12(S)-hydroxy-5,8,10,14-eicosatetraenoic acid. In addition, four other nonlabeled metabolites, formed from endogenous substrates, were detected in ovarian extracts. Their structures, determined by mass spectrometric analysis, were the corresponding 11- and 12-hydroxy analogs formed from eicosapentaenoic acid (11-HEPE and 12-HEPE) and 9-hydroxy-6,10,12,15-octadecatetraenoic acid (9-HOTE) and 13-hydroxy-6,9,11,15-octadecatetraenoic acid formecl from stearidonic acid. The biosynthesis of the 11 - and 12-hydroxy products was calcium dependent, localized to the 100,000 x g supernatant cell fraction, and was inhibited by nordihydroguaiaretic acid, but not inhibited by the prostaglandin synthase inhibitors aspirin and indomethacin, or the monoxygenase inhibitor proadifen. Together these data suggested that both the 11 (R)- and 12(S)-hydroxy products were formed from lipoxygenase-type enzymes. Incubation of homogenates of immature ovaries with eicosapentaenoic acid revealed the major product to be I2-HEPE, whereas in mature ovaries mainly 11-HEPE was formed. Extraction of spawned eggs with methanol revealed that predominantly 11-HEPE and 9-HOTE were formed from endogenous substrates. This study shows that female gonads of the mussel express an 11(R)- and 12(S)-lipoxygenase activity whose expression is dependent on differentiation of the ovary.