TrypanosomaParasitic protozoans have been extensively invest

TrypanosomaParasitic protozoans have been extensively investigated due to the search for new effective drugs for the dangerous diseases they cause. Because mammalian mitochondria do not possess alternative dehydrogenase in the respiratory chain, these proteins have become a specific potential target for disease treatment. The African trypanosome T. brucei, the causal agent of sleeping sickness in humans and nagana in cattle, has a dual life cycle in the bloodstream of the mammalian host and the insect vector (Bienen et al., 1991, Hajduk et al., 1992). In the mammalian bloodstream, the trypanosomes exist as dividing long slender forms that lack well-developed mitochondria, cytochromes, and cyanide-sensitive electron transport. In these developmental forms, energy requirements are provided completely by glycolysis using glucose from the blood of the mammalian host (Opperdoes 1987). However, the procyclic forms, present in the midgut of the insect host, possess a single, large mitochondrion containing respiratory chain complexes generally similar to those present in eukaryotes (Hajduk et al. 1992). In 2003, an alternative NADH dehydrogenase from the T. brucei procyclic form (NDH2) was isolated and characterized (Fang and Beattie 2003b). The enzyme is rotenone-insensitive and contains noncovalently bound FMN as a cofactor, instead of the FAD usually present in eukaryotic type II dehydrogenases. FMN appears to serve as one electron donor to UQ or oxygen in Methylprednisolone to the two-electron reduction conducted by FAD. This feature fosters ROS production, since superoxide is generated by a one-electron reduction of molecular oxygen. A previous study confirmed that the rotenone-insensitive NADH dehydrogenase is a potential source of superoxide production in procyclic trypanosome mitochondria (Fang and Beattie 2002b). The T. brucei alternative NADH dehydrogenase is a dimer of 65kDa, which separates into two 33kDa subunits, and is located on the inner mitochondrial membrane facing the matrix (Fang and Beattie 2003b). Because of a low Complex I activity, one of possible functions for NDH2 in T. brucei mitochondria is to complement Complex I, mediating electron transfer from internal NADH to the respiratory chain. Subsequent studies on the requirement for the core subunits of Complex I in the T. brucei respiratory chain lead to conclusion that Complex I activity can be fully replaced by NDH2 (Verner et al. 2013). In addition, the enzyme is capable of utilizing deamino NADH and NADPH as substrates in vitro (Fang and Beattie 2003b). Interestingly, the mitochondria of the procyclic T. brucei depleted of Complex I subunits exhibit an increased sensitivity of the NADH oxidation to diphenyloiodonium chloride (IDP) and a lower sensitivity to rotenone, a specific inhibitor of Complex I (Verner et al. 2011). However, the depletion of NDH2 affects both cell growth and the mitochondrial membrane potential, although the remaining activities of the respiratory complexes are unaltered with an exception of the increased activity of glycerol-3-phosphate dehydrogenase (Verner et al. 2013). These results support the hypothesis that in the procyclic T. brucei mitochondrion, NDH2 might be preferentially used to regenerate NAD+ and maintain the mitochondrial membrane potential compared to Complex I.