Roles of triosephosphate isomerase and aerobic metabolism in Trypanosoma brucei

Kinetoplastid protozoa compartmentalize the first seven enzymes of glycolys is acid two enzymes of glycerol metabolism in a microbody, the glycosome. W hile in its mammalian host, Trypanosoma brucei depends entirely on glucose for ATP generation. Under aerobic conditions, most of the glucose is metabo lized to pyruvate, Aerobic metabolism depends on the activities of glycosom al triosephosphate isomerase and a mitochondrial glycerophosphate oxidase, and on glycerophosphate <----> dihydroxyacetone phosphate exchange across t he glycosomal membrane. Using a combination of genetics and computer modell ing, we show that triosephosphate isomerase is probably essential for blood stream trypanosome survival, but not for the insect-dwelling procyclics, wh ich preferentially use amino acids as an energy source. When the enzyme lev el decreased to about 15 % of that of the wild-type, the growth rate was ha lved. Below this level, a lethal rise in dihydroxyacetone phosphate was pre dicted. Expression of cytosolic triosephosphate isomerase inhibited cell gr owth. Attempts to knockout the trypanosome alternative oxidase genes (which are needed for glycerophosphate oxidase activity) were unsuccessful, but w hen we lowered the level of the corresponding mRNA by expressing a homologo us double-stranded RNA, oxygen consumption was reduced fourfold and the rat e of trypanosome growth was halved.