GLUTATHIONE-REDUCTASE AND GLUTAMATE-DEHYDROGENASE OF PLASMODIUM-FALCIPARUM, THE CAUSATIVE AGENT OF TROPICAL MALARIA

The use of glutathione reductase inhibitors in chemotherapy is the rai son d'etre for this study. Two enzymes were purified to homogeneity fr om the intraerythrocytic malarial parasite Plasmodium falciparum: glut athione disulfide reductase, an antioxidative enzyme, which appears to play an essential role for parasite growth and differentiation, and g lutamate dehydrogenase, an enzyme not occurring in the host erythrocyt e. The two proteins were copurified and separated by gel electrophores is with yields of approximately 20%. Malarial glutathione reductase, a homodimer of 110 kDa with a pH optimum of 6.8 and a high preference f or NADPH over NADH, was shown to contain FAD as its prosthetic group. The N-terminal sequence, VYDLIVIGGGSGGMA, which can be aligned with re sidues 20-34 of human glutathione reductase, represents the first beta strand and the diphosphate-fixing helix of the FAD domain. Glutamate dehydrogenase was confirmed as a hexamer with blocked N-termini; it is an enzyme that is highly specific for NADP and NADPH. The copurificat ion of the proteins and the potential of P. falciparum glutathione red uctase as a drug target are discussed.