Lactate dehydrogenase from the northern krill Meganyctiphanes norvegica: comparison with LDH from the Antarctic krill Euphausia superba

Electrophoretic polymorphism of lactate dehydrogenase (LDH, EC 1.1.1.27) fr om abdominal muscle is reported in the northern krill Meganyctiphancs norve gica. In the population, from the Gullmarsfjord (west coast of Sweden), LDH was encoded for by two different Ldh-A* and -B* loci. The isoenzymes were named according to their electrophoretic mobilities. Ldh-A* locus was polym orphic. The allelic frequencies were a = 0.99, a' = 0.002, a'' = 0.004, a'' ' = 0.004. The level of LDH polymorphism is low. Most individuals possess t he same amount of two LDH homopolymers (LDH-A*(4) and LDH-B*(4)). The Megan yctiphanes norvegica LDH-A*(4) and LDH-B*(4) isoenzymes and the predominant LDH-A*(4) isoenzyme from Euphausia superba were purified to specific activ ities of 294, 306 and 464 mu mol NADH min(-1) mg(-1), respectively. In both species the LDH isoenzymes were separated by chromatofocusing. All three i soenzymes are L-specific tetramers with molecular weight of approximately 1 60 kDa. Northern krill LDH-A*(4) has higher affinity for pyruvate and lacta te and is more thermostable than LDH-B*(4). Both isoenzymes are inhibited s ignificantly by high concentration of pyruvate but not lactate. Antarctic k rill isoenzyme exhibits high substrate affinities, high NAD inhibition, hig h inhibition at 10 mM pyruvate, lack of lactate inhibition, and high heat s tability and resembles northern krill LDH-A*(4) isoenzyme. (C) 2001 Elsevie r Science Inc. All rights reserved.