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Received March 2, 2009; Revision received October 19, 2009
Energy metabolism of Leishmania donovani parasite has been investigated under conditions imitating intralysosomal-like environment in the host organism. Trans-plasma membrane electron transport and oxygen uptake were inhibited progressively when promastigote cells were exposed to pH 5.5 and 37°C. A special feature of the respiratory chain in amastigote was the absence of complex I, II, and IV. When L. donovani was grown at pH 5.5 and 37°C, the acid excretory product succinate was increased in comparison to cells grown at pH 7.5 and 24°C. The findings of this study showed that the amastigote form catabolized fatty acid to excrete succinic acid when oxidative phosphorylation was impaired. Amastigote mitochondria failed to generate membrane potential by oxidizable substrates. On the other hand, the amastigote cell showed absorbance change of safranine O when fatty acid was the oxidizable substrate. The safranine signal was completely reversed by valinomycin, carbonyl cyanide 4-(trifluromethoxy)phenylhydrazone, malonate, and oxaloacetate. Our data suggest that the generation of metabolic energy from succinate/H+ efflux will contribute to energy requiring process of amastigote significantly. On the basis of these results, we conclude that due to absence of oxidative phosphorylation in amastigotes, energy linked functions in amastigotes might occur through fumarate reduction leading to ΔpH generation by succinate excretion.
KEY WORDS: Leishmania donovani promastigote and amastigote, mitochondria, differentiation, stage specific