Fig. 1.

Effects of complex II inhibitors, malonate and atpenin A5, on rates of H₂O₂ production by rat skeletal muscle mitochondria oxidizing palmitoylcarnitine alone and in combination with carnitine or malate. (A) Typical traces of H₂O₂ production during palmitoylcarnitine oxidation and effects of complex II inhibitors. Palmitoylcarnitine (PC) was added after 5 min incubation of mitochondria (0.3 mg protein · ml⁻¹) with the Amplex UltraRed detection system plus exogenous SOD. The background rates in the absence of substrate were subtracted from all rates after substrate addition. Numbers by the traces represent rates of H₂O₂ production in pmol · min⁻¹ · mg protein⁻¹ after calibration by addition of known amounts of H₂O₂. The addition of atpenin A5 increased the rate of H₂O₂ production during oxidation of palmitoylcarnitine from 27 ±1 (n=6) to 105±5 (n=4) pmol · min⁻¹ · mg protein⁻¹. After addition of malonate it decreased to 7±1 pmol · min⁻¹ · mg protein⁻¹ (n=4). Subsequent numbers are rates for the presented traces (n=1). (B) Effects of malonate addition on the rates of H₂O₂ production during oxidation of substrates from Table 1. Open bars, no malonate added; shaded bars, 0.5 mM malonate added after substrate. Values are means ± SEM. n=4 (PC ± malonate), n=6 (PC + carnitine ± malonate), n=5 (PC + malate ± malonate). p values were calculated using an unpaired Student t test.