Carbon dioxide fixation in malaria (Plasmodium iophurae).

Abstract

THE main function of the mature erythrocyte is the transport of oxygen to and the removal of carbon dioxide from the tissues. The obligate intraerythrocytic parasite, malaria, not only requires constituents of the red blood cell such as haemoglobin and glucose, but also the gases transported by its host cell. The role of oxygen in the metabolism of the malaria parasite is well documented, and stems from the early observation that in vitro blood infected with malaria soon loses its bright red appearance and darkens1. Aerating the cells restores the brightness, and the parasites continue to maintain themselves by utilizing the oxyhaemoglobin for aerobic metabolism. In spite of the fact that infected erythrocytes and even erythrocyte free malaria parasites consume oxygen in the presence of suitable substrates, only 25–50 per cent of the available glucose is aerobically degraded to carbon dioxide and water2. Thus, malaria parasites are principally facultative aerobes and the best gas mixture for maintaining parasitized erythrocytes in vitro is 95 per cent air + 5 per cent carbon dioxide3. By contrast, the role of carbon dioxide in the metabolism of malaria is not well understood and is restricted to a single, equivocal record some 20 years ago4. The present communication presents unequivocal evidence for a functional role of carbon dioxide in the metabolism of malaria parasites and erythrocytes infected with malaria.