The sulphur requirements of the erythrocytic form of Plasmodium knowlesi

Abstract

Growth of the malaria parasite Plasmodium knowlesi on S35-labelled erythrocytes in vivo indicated that about 80% of the methionine introduced into its protein was derived from that in the red-cell globin. The (S35) methionine was converted into (S35) cystine in vitro to provide a source of cystine sulfur for the parasite in addition to that already present in the hemoglobin and glutathione of the erythrocyte. Estimates of the extent to which these sources contribute to the cystine requirement of the parasite were made. Under identical in vitro conditions the uptake of DL-(S35) methionine by parasitized erythrocytes was markedly greater than that of DL-(S35) cysteine. 6.0 and 2.4 times as much methionine and cystine, respectively were found in the hemoglobin of a monkey erythrocyte as in the protein of a mature parasite. The implications of this observation in the nutrition of the parasite are discussed.