Metabolic Transformation of Trypanosoma rhodesiense in Culture

Abstract

THE pathogenic African trypanosome, Trypanosoma rhodesiense, has three morphological cell types in the mammalian bloodstream—long slender (LS), intermediate short stumpy (ISS) and short stumpy (SS). The terminal respiration of the LS forms is independent of cytochrome pigments¹ and is effected by L-glycerol-3-phosphate oxidase² located in discrete extramitochondrial particles³. A functional citric acid cycle is absent⁴ and there is a promitochondrion in the form of a single canal with no cristae⁵. Vickerman^5,6 has shown that in the transition of LS to SS forms, cristae and NADH-tetrazolium reductase activity develop within the mitochondrial tubule which may be related to the acquired ability of these stages to oxidize a-oxoglutarate^5,7,8. These results suggested that a respiratory switch to intramitochondrial oxidation had occurred. Bowman et al.⁹, however, demonstrated that this switch is unlikely to be complete, for the SS forms do not possess all the enzymes of the citric acid cycle nor were cytochromes detectable. In contrast the culture (epimastigote) form derived from the SS congener has developed a functional citric acid cycle¹⁰, a cytochrome mediated electron transport system¹¹ and a single complex mitochondrion⁶. It seems that mitochondrial activation is initiated in the mammalian bloodstream but is not completed until transfer into culture. This report describes the sequence of metabolic changes associated with the acquisition of mitochondrial mediated metabolism during transformation into culture forms.