Fasciola hepatica: The subcellular distribution and kinetic and electrophoretic properties of malate dehydrogenase

Abstract

The optimal pH for oxalacetate reduction was 9.0 for the mitochondrial and supernatant enzyme. The optimal pH for malate oxidation was 10 for both fractions. Maximal activity during oxalacetate reduction was 3.26 ± 0.26 μmoles of NADH oxidized/mg of protein/min and 3.02 ± 0.27 for the supernatant and mitochondrial fractions, respectively. Maximal malate oxidation was 0.495 ± 0.08 and 0.72 ± 0.12 (not statistically different) for the supernatant and mitochondrial fractions, respectively. High concentrations of malate inhibited activity to a greater extent in the supernatant fraction while oxalacetate inhibited activity to a greater extent in the mitochondrial fraction. The supernatant malate dehydrogenase was more heat stable than the mitochrondrial enzyme. Electrophoresis showed three isoenzymes of malate dehydrogenase in whole homogenates of Fasciola hepatica and all three were represented in the supernatant while only one band was seen in the mitochondrial fraction. The presence of two types of malate dehydrogenase, one in the supernatant with three isoenzymes and one in the mitochondria with one isoenzyme, is proposed.