Figure 1.

Effects of superoxide on proton conductance of kidney (a and c) and spleen (b and d) mitochondria isolated from WT (a and b) and UCP2-deficient (c and d) mice. Proton leak titration was performed with or without addition of a superoxide-generating system (xanthine plus xanthine oxidase), essentially as described previously (30) and in Methods. Graphs show the rate of proton leak as a function of its driving force, mitochondrial membrane potential. Open squares, control; filled squares, xanthine (50 μM) plus xanthine oxidase (0.2 mU/3.5 ml for kidney mitochondria, 0.1 mU/3.5 ml for spleen mitochondria); open circles, xanthine/xanthine oxidase plus 500 μM GDP. Western blot analysis confirmed that UCP2 protein was present in kidney (e) and spleen mitochondria (8) of WT mice, and that UCP2 protein was absent in mitochondria from UCP2 KO mice. Proton leak data are means ± SEM of three independent experiments.