Effects of 3,5-Dihalogenated-4-hydroxybenzonitriles on the Activity of Mitochondria From White Potato Tubers.

Effects of the herbicide 3,5-diiodo-4-hydroxybenzonitrile (ioxynil), and its dibromo and dichloro analogs, upon the respiration of mitochondria isolated from white potato tubers (Solanum tuberosum L.) were investigated. Mitochondrial-mediated oxygen uptake was monitored polarographically with a platinum oxygen electrode.With succinate as substrate for mitochondrial oxidation, ioxynil stimulated both ADP-limited and ADP + phosphate-deficient oxygen utilization. Ioxynil also circumvented oligomycin-inhibited respiration and slightly stimulated mitochondrial ATPase activity. Responses produced by ioxynil on respiration were similar to, but occurred at lower concentrations than, those of 2,4-dinitrophenol.The dibromo- and dichloro-substituted analogs of ioxynil also stimulated ADP-limited respiration and released oligomycin-inhibited oxygen uptake. Based on concentration, the decreasing order of uncoupling activity was I > Br > Cl with respect to the halogen substituents.