INTERMEDIATE METABOLISM IN TRYPANOSOMA-CRUZI

Epimastigotes of Trypanosoma cruzi, the causative agent of Chagas disease, catabolize proteins and amino acids with production of NH3, and glucose with production of reduced catabolites, chiefly succinate and L-alanine, even under aerobic conditions. This ''aerobic fermentation of glucose'' is probably due to both the presence of low levels of some cytochromes, causing a relative inefficiency of the respiratory chain for NADH reoxidation during active glucose catabolism, and the lack of NADH dehydrogenase and phosphorylation site I, resulting in the entry of reduction equivalents into the chain mostly as succinate. Phosphoenol pyruvate carboxykinase and pyruvate kinase may play an essential role in diverting glucose carbon to succinate or L-alanine, and L-malate seems to be the major metabolite for the transport of glucose carbon and reduction equivalents between glycosome and mitochondrion. The parasite contains proteinase and peptidase activities. The major lysosomal cysteine proteinase, cruzipain, has been characterized in considerable detail, and might be involved in the host/parasite relationship, in addition to its obvious role in parasite nutrition. Among the enzymes of amino acid catabolism, two glutamate dehydrogenases (one NADP- and the other NAD-linked), alanine aminotransferase, and the major enzymes of aromatic amino acid catabolism (tyrosine aminotransferase and aromatic cr-hydroxy acid dehydrogenase), have been characterized and proposed to be involved in the reoxidation of glycolytic NADH.