Properties and function of malate enzyme from Dicentrarchus labrax L. liver.

Malate enzyme (L-malate:NADP+ oxidoreductase (oxaloacetate decarboxylating, EC 1.1.1.40) has been purified from Dicentrarchus labrax liver to 99% homogeneity by gel filtration, anion exchange and affinity chromatographies. The apparent molecular weight was estimated by gel filtration chromatography to be 148,000. Analysis of the enzyme on sodium dodecyl sulphate polyacrylamide disc gel electrophoresis was shown to be a tetrameric protein. The purified enzyme showed a pH optimum 8.5 (Tris-HCl buffer) and required bivalent cations for catalysis. The temperature-activity relationship for the enzyme showed broken Arrhenius plots with inflexions at 15 and 40 degrees C. Kinetic properties and the effects of some metabolites related to L-malate are studied.