B-NPOx did not inhibit the activity of purified HADH-isozyme II but did exhibit an inhibitory effect towards T. cruzi homogenates. (A) Effects of B-NPOx, Et-NPOx, NPOx and N-ethylmaleimide (0.05–1 mM) on the activity of purified HADH-isozyme II in the presence of 5 mM α-ketoisocaproate and 0.12 mM NADH. Changes in the absorption at 340 nm were recorded over a 5 min period. The enzymatic activity was expressed as a percentage of ΔE 340 nm/min, where Vmax was 100%. (B) Effects of B-NPOx, B-NPOx + N-ethylmaleimide, Et-NPOx, Et-NPOx + N-ethylmaleimide and NPOx (0.05–1 mM) on the enzymatic activities of the T. cruzi homogenates. The N-ethylmaleimide concentration was 1 mM and the reaction conditions were set as in (A). As controls, the effects of B-NPOx, Et-NPOx and NPOx on the T. cruzi homogenates were assayed in the absence of α-ketoisocaproate. The kinetic assays have been reported as the mean values ± the standard deviation from three independent experiments.