Terminal oxidases in the trypanosomatid Trypanosoma cruzi

Abstract

1. 1. Titration of Trypanosorna cruzi respiration with cyanide, with results treated as Dixon plots, indicated the presence of several terminal oxidases. 2. 2. The inhibitions obtained at low cyanide concentrations (0–300 μM), taken together with cyanide effects on cytochrome aa 3-deficient, dyskinetoplastic epimastigotes, supported cytochrome aa 3 as T. cruzi main terminal oxidase. 3. 3. By increasing cyanide concentration to 1.0 mM, two alternative terminal oxidases could be detected. One of these was (a) active in both kinetoplastic and dyskinetoplastic (cytochrome aa 3-deficient) epimastigotes, and (b) azide- and antimycin-insensitive. 4. 4. Complementary cytochrome studies with intact epimastigotes and mitochondrial membranes revealed the presence of cytochromes aa 3, b, c 558 , o and possibly d, as components of the parasite electron transport system. Fractionation studies demonstrated that both o and d were bound to the mitochondrial membrane. 5. 5. Reduction by endogenous substrates and complex formation with cyanide supported cytochrome o as alternative terminal oxidase. 6. 6. EB-cultured, dyskinetoplastic epimastigotes showed the same respiration rate as the kinetoplastic cells, despite the significant decrease of cytochrome aa 3, thus indicating adaptive mechanisms that determine the expression of alternative oxidases, whenever the main terminal activity is depressed.