D-LACTATE PRODUCTION IN ERYTHROCYTES INFECTED WITH PLASMODIUM-FALCIPARUM

The production of d-lactate that accompanies the metabolism of glucose to l-lactate in Plasmodium falciparum was evaluated with erythrocytes that contained either young or mature parasites. Infected cells with ring-stage parasites release l-lactate and d-lactate at rates 1340 and 81 nmol h-1 (108 cells)-1, respectively. These rates increase to 2050 and 136 nmol h-1 (108 cells)-1, respectively, in infected cells with trophozoite/schizont-stage parasites. d-Lactate represents 6-7% of the total lactate. The formation of d-lactate is by way of a methylgloxal pathway in which methylglyoxal is formed nonenzymatically from dihydroxyacetone phosphate and is then converted into d-lactate by the sequential action of parasite glyoxalase I and glyoxalase II. The kinetic properties of parasite glyoxalase I and glyoxalase II allow these enzymes to be distinguished from those in the host cell. d-Lactate production by the parasite appears to be a defense mechanism to protect the parasite from the toxic effects of methylglyoxal. © 1990.