MITOCHONDRIAL ELECTRON TRANSPORT IN AFRICAN TRYPANOSOMES

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Energy production in the rapidly dividing forms of pathogenic African trypanosomes is totally dependent upon glycolysis. This normally depends on an unusual mitochondrial electron transport system and when this is not operating on an unusual method of glycerol production. In the long slender bloodstream trypanosome tbe electron transport system contains only two enzymes, glycerol-3-phosphate dehydrogenase and the trypanosome alternative oxidase (TAO). The TAO and the production of glycerol are two metabolic steps not shared by the host but essential to the parasite. These steps are, therefore, ideal targets for chemotherapy. The production of glycerol is thought to be by a reversal of glycerol kinase but little is known of the TAO other than its similarity to the alternative oxidase of some higher plants, fungi and algae. For this reason, we plan a study of the TAO and its inhibitors. The information gained is expected to allow clear biochemical differences between host and parasite to be exploited leading to a highly selective therapy. Trypanosoma brucei brucei will be used as a model to achieve two primary objectives. The first is to isolate, characterize, and finally reconstitute the electron transport system. The second is to evaluate a limited number of inhibitors for utility as drug candidates. The glycerol-3-phosphate dehydrogenase and the TAO components of the electron transport chain will be released from the mitochondrial membranes of T. b. brucei bloodstream cells. They will be separated and then a functioning system will be reconstituted from the isolated components. A study will be made of the mechanism whereby the oxidase component of the chain is inhibited, the resulting information being used in the eventual design of improved inhibitors. A promising lead for a practical inhibitor of the TAO has developed: the N-n-alkyl 3,4dihydroxybenzamides. A high cure rate has been achieved with one of these, N-n-butyl 3,4dihydroxybenzamide. This compound will be evaluated further and several closely related compounds will be examined for utility as chemotherapeutic agents.