Electron microscopic observation of Trypanosoma cruzi epimastigotes reveals the presence of microbody-like structures (microperoxisomes) in which 3,3'-diaminobenzidine (DAB) is peroxidized to electron-opaque material. The role of peroxidase in DAB peroxidation is supported by the enzyme demonstration in disrupted epimastigotes and the microbody-containing cell fractions.

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SYNOPSIS The epimastigote or culture form of Trypanosoma cruzi oxidizes [3‐14C] pyruvate and [2‐14C] acetate to 14CO2 without an apparent increase in overall respiration. This oxidation takes place through the tricarboxylic acid cycle as shown by (a) the incorporation of substrate 14C into cycle intermediates; (b) the earlier liberation of acetate carboxyl carbon as CO2; and (c) the characteristic intramolecular distribution of pyruvate and acetate carbon atoms in the skeletal carbon of aspartic and glutamic acids. Upon oxidation of [3‐14C] pyruvate and [2‐14C] acetate, two of the products, alanine and glutamic acid, are found to account for more than 50% of incorporated 14C; labeling of alanine predominates with [3‐14C] pyruvate while labeling of glutamic acid predominates with [2‐14C] acetate. Using [1‐ or 6‐14C] glucose as substrate, the pattern of 14C distribution in soluble metabolites closely resembles that obtained with [3‐14C] pyruvate, in accordance with the joint operation of the Embden‐Meyerhof pathway and Krebs cycle. The cycle operation depends on electron transport through the mitochondrial respiratory chain, since antimycin A, at a relatively low concentration, inhibits the oxidation of [2‐14C] acetate to 14CO2, to the same extent as the parasite respiration. Though functional in T. cruzi epimastigotes, the oxidative role of the Krebs’ cycle is apparently limited by the absence of an efficient oxidative apparatus. The cycle operation does, however, constitute an important source of skeletal carbon for the biosynthesis of amino acids and can contribute to the process of glycogenesis.

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