Fig. 3.

Identification of the inhibition site of SQ in the respiratory chain of Leishmania. (A) Traces represent the oxygen consumption rates of L. donovani promastigotes in the presence of 5 mM succinate. Arrows indicate the addition of appropriate substrates and inhibitors at their respective final concentrations, namely, 60 μM digitonin, 100 μM ADP, 0.1 mM TMPD plus 1.7 mM ascorbate, 1 mM KCN, 2 mM malonate, 6.7 mM α-glycerophosphate (α-GP), and 250 μM SQ. (B) SDH activity in the presence of increasing concentrations of SQ. Activity was measured by the decrease of absorbance at 415 nm due to the reduction of ferricyanide by the SDH activity of the mitochondrial fraction in the presence of succinate, as described in Materials and Methods. Error bars indicate the SD. Samples not treated with SQ (c) and samples in the presence of malonate (M), an SDH inhibitor, were used as positive and negative controls, respectively. Activity was measured at 37°C.