GLUCOSAMINE 6-PHOSPHATE DEAMINASE IN PLASMODIUM-FALCIPARUM

The pathways of glucose utilization for energy production in the malar ia parasite, Plasmodium falciparum, have been studied extensively. Lit tle is known, however, about the reactions by which glucose is convert ed into complex carbohydrates in the parasite, and knowledge of the ca tabolism of these substances is likewise scanty. The present investiga tion was undertaken to determine whether the parasites possess a key e nzyme of glucosamine catabolism, i.e. glucosamine 6-phosphate deaminas e (EC 5.3.1.40), which catalyses the conversion of the sugar phosphate to fructose 6-phosphate and ammonia. Lysates of Plasmodium-infected e rythrocytes had substantially higher deaminase activity than control s amples from normal erythrocytes, and an even higher specific activity was observed in extracts of isolated parasites, amounting to 20-40 tim es that of uninfected cells. Anion exchange chromatography indicated t hat the parasite deaminase eluted in a retarded position when compared to the elution profile of the erythrocyte enzyme. The charge differen ce suggested by these findings was established more directly by chroma tofocusing, which indicated pI values of 6.85 and 8.55 for the parasit e and erythrocyte deaminases, respectively. Other differences were als o observed, notably a greater thermolability on the part of the parasi te enzyme. These results indicated that the parasites synthesize a spe cific deaminase that is distinct from the normal erythrocyte enzyme. S tudies on synchronized parasite cultures further indicated that the pa rasite deaminase is developmentally regulated, because a dramatic incr ease in activity levels occurred during the later stages of parasite d evelopment.