Kinetic characterization of mitochondrial malate dehydrogenase from Dictyostelium discoideum.

Malate dehydrogenase (MDH; EC 1.1.1.37) from Dictyostelium discoideum was purified and characterized MDH activity from whole cells was purified 275-fold. The mitochondrial and cytoplasmic MDH present co-purified through three ion exchange and affinity chromatography steps. The isoenzymes were barely separable by either disc gel electrophoresis or isoelectric focusing. The purified preparation containing both isoenzymes had a single pH optimum (9.3-9.5) and an apparent molecular weight of 70000. It exhibited linear kinetics and responded to known inhibitors of MDH, i.e. thyroxine and hydroxymalonate. Michaelis and dissociation constants obtained with this preparation were similar to those obtained with a 10-fold purified mitochondrial MDH.