Oxidant defense enzymes of Plasmodium falciparum.

We have measured and characterized three oxidant defense enzymes in early and late intraerythrocytic stages of the human malarial parasite, Plasmodium falciparum. Isolated early intraerythrocytic stages contain catalase (24.1 mumol min-1 (mg protein)-1) and superoxide dismutase (SOD; 6.3 units (mg protein)-1) but little or no glutathione peroxidase (GPX; less than 2 mumol min-1 (mg protein)-1). Isolated late intraerythrocytic stages of P. falciparum contain slightly less catalase (17.0 mumol min-1 (mg protein)-1) but significantly more GPX (7.7 mumol min-1 (mg protein)-1) and SOD (25.1 units (mg protein)-1). P. falciparum, like P. berghei, probably acquires most of its SOD from its host, since parasite-associated SOD is predominantly cyanide-sensitive, and has the same pI as host SOD. Unlike P. berghei, however, late stages of P. falciparum contain an additional SOD isozyme which is not cyanide-sensitive and may represent an endogenous enzyme. Parasites grown in red cells that have been partially depleted of SOD are more sensitive to exogenously generated superoxide, suggesting some dependence of the parasite on host SOD.