Abstract
1. 1. The ADP plus P i-stimulated oxidation of succinate by mitochondria from the insect trypanosomatid Crithidia fasciculata was maximally inhibited (64%) by suramin at a concentration (60 μM) which did not affect the electron transport uncoupled by FCCP.‡ Inhibition of the latter required a considerably higher concentration of the drug, 50% inhibition being attained at about 0.8 mM. 2. 2. ATP synthesis by mitochondrial particles was inhibited by suramin, 50% inhibition being attained at about 50 μM. This inhibition was strictly competitive towards ADP, but it was not linearly competitive, since a secondary plot of apparent K m values vs concentration of the drug was strongly concave upwards. 3. 3. The FCCP-stimulated ATPase activity of the mitochondrial particles was completely abolished either by oligomycin (20 μg/ml) or by 200 μM suramin. 4. 4. The results suggest that oxidative phosphorylation may be a primary target for the trypanocide effect of suramin on organisms having, like C. fasciculata, a well-developed respiratory chain.
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