PURIFICATION AND PROPERTIES OF PLASMODIUM-FALCIPARUM MALATE-DEHYDROGENASE

Asexual intraerythrocytic Plasmodium falciparum were shown to have a single isoenzyme of malate dehydrogenase. This malate dehydrogenase was purified to apparent homogeneity using a three-step purification protocol. The parasite malate dehydrogenase had an apparent subunit molecular weight of 32 kDa, a pH optimum of 7.0 for the reduction of oxaloacetate, and a sharp thermal transition between 40-degrees-C and 45-degrees-C. These characteristics distinguish P. falciparum malate dehydrogenase from both the cytoplasmic and mitochondrial malate dehydrogenase isoenzymes of humans. In addition, the resistance of the parasite malate dehydrogenase to substrate inhibition by oxaloacetate suggests that it is the cytoplasmic malate dehydrogenase isoenzyme. The apparent absence of mitochondrial malate dehydrogenase from asexual intraerythrocytic P. falciparum contributes to evidence indicating that the mitochondrion is undeveloped at this stage of the parasite's life cycle.