The sulphur requirements of the erythrocytic from of Plasmodium knowlesi.

Until the discovery by Knowles & Das Gupta (1932) of a malaria parasite virulent for rhesus monkeys, the study of mammalian malaria in the laboratory was seriously hampered. This parasite, which is mildly infective to man, was named Plakenwdium knowlesi by Sinton & Mulligan (1932). Although extensive studies have been made on the culture and metabolism of the erythrocytic form of P. knowlesi (for reviews see McKee, 1951 and Fulton, 1951), little is known about the extent to which the parasite can satisfy its nutritional requirements from the cytoplasmic content of its host cell, the erythrocyte. The growth of the parasite in the erythrocyte is associated with a reduction in the haemoglobin content and the formation of parasite pigment. This pigment has been identified as haematin (Morrison & Anderson, 1942; Rimington & Fulton, 1947) and is derived from the haem moiety of globin, the total pigment (haem plus haematin) content of the parasitized cell remaining constant (Ball, McKee, Anfinsen, Cruz & Geiman, 1948). In contrast, the total nitrogen of the infected erythrocyte decreases, and this loss has been attributed to the hydrolysis of globin by the parasite and the utilization of about half the products of hydrolysis for the synthesis of its own protein (Morrison & Jesky, 1948; see also McKee, 1951). In spite of this apparent excess of available amino acids, an additional source of methionine appears to be essential for the growth of P. knowlesi both in vitro and in vivo (McKee, Geirnan & Cobbey, 1947; Geiman & McKee, 1948). The reasons for this specific requirement are not known, but it has been suggested that the low methionine content of haemoglobin may make it necessary for the parasite to draw on the plasma for additional supplies of this amino acid (McKee, 1951). The present paper is concerned with the sulphurcontaining compounds within the monkey erythrocyte, and their utilization by the parasite for the synthesis of its own protein.