Oxidative Phosphorylation, Ca Transport, and Fatty Acid-induced Uncoupling in Malaria Parasites Mitochondria*

Respiration, oxidative phosphorylation, calcium uptake, and the mitochondrial membrane potential of trophozoites of the malaria parasite Plasmodium berghei were assayed in situ after permeabilization with digitonin. ADP promoted an oligomycin-sensitive transition from resting to phosphorylating respiration. Respiration was sensitive to antimycin A and cyanide. The capacity of trophozoites to sustain oxidative phosphorylation was additionally supported by the detection of an oligomycin-sensitive decrease in mitochondrial membrane potential induced by ADP. Phosphorylation of ADP could be obtained in permeabilized trophozoites in the presence of succinate, citrate, a-ketoglutarate, glutamate, malate, dihydroorotate, a-glycerophosphate, and N,N,N*,N*-tetramethyl-p-phenylenediamine. Ca uptake caused membrane depolarization compatible with the existence of an electrogenically mediated Ca transport system in these mitochondria. An uncoupling effect of fatty acids was partly reversed by bovine serum albumin, ATP, or GTP and not affected by atractyloside, ADP, glutamate, or malonate. Evidence for the presence of a mitochondrial uncoupling protein in P. berghei was also obtained by using antibodies raised against plant uncoupling mitochondrial protein. Together these results provide the first direct biochemical evidence of mitochondrial function in ATP synthesis and Ca transport in a malaria parasite and suggest the presence of an H conductance in trophozoites similar to that produced by a mitochondrial uncoupling protein.