Enzyme activities in fish spermatozoa with focus on lactate dehydrogenase isoenzymes from herring Clupea harengus

The activities of NAD- and NADP-dependent dehydrogenases and creatine kinase were compared in extracts of spermatozoa from herring (Clupea harengus), carp (Cyprinus carpio) and catfish (Clarias gariepinus). The activity of malic enzyme in herring spermatozoa was approximately 5 and 36 times higher than in carp and catfish spermatozoa. In contrast, lactate dehydrogenase activity in herring spermatozoa was very low. Herring spermatozoa possess two isoenzymes of lactate dehydrogenase: LDH-A(2)B(2) and LDH-B(4). Both herring spermatozoa isozymes were separated, partly purified and characterized by kinetic and physico-chemical properties. The pH optima and K(m) values for pyruvate reduction were 7.1, 7.25, 7.6 and 0.22, 0.07, 0.09 mM for LDH-A(4), LDH-A(2)B(2) and LDH-B(4), respectively. The isoenzymes also have different thermostabilities. High activity of malic enzyme in herring spermatozoa suggests adaptation to metabolism at high oxygen tension.