Purification and properties of malic enzyme from herring Clupea harengus spermatozoa

Herring spermatozoa exhibit higher activity of malic enzyme (ME) than Atlantic salmon (Salmo salar), brown trout (Salmo trutta), carp (Cyprinus carpio) and African catfish (Clarias gariepinus) spermatozoa. Two molecular forms of ME are present in herring spermatozoa: an NAD-preferring malic enzyme with very high activity and an NADP-specific malic enzyme with much lower activity (ratio about 33:1). NAD-preferring ME was purified by chromatography on DEAE-Sepharose, Red Agarose and Sephadex G-200 to a specific activity of 36 μmol/min/mg protein and NADP-specific ME on DEAE-Sepharose and 2′5′-ADP Sepharose. The molecular mass for NAD-preferring and NADP-specific ME determined by SDS-PAGE was equal to 61 and 64 kDa, respectively. High activity of ME suggests adaptation of herring spermatozoa to metabolism at high oxygen tension for herring spawn.