[Interaction of ubisemiquinone with the high-potential iron-sulfur center of submitochondrial particle succinate dehydrogenase. EPR study at 240 and 12 degrees K].

The ESR spectra of beef heart submitochondrial particles were measured in the same samples at 240 degrees and 12 degrees K. There is close similarity between the inhibitory action of alpha-thenoyltrifluoroacetone, ethanol and ferricyanide on the non-saturating free radical signal SQ-2 observed at 240 degree K and peak at g=1.99 (and 2.04) which is visible only at very low temperatures. This result strongly supports our previous proposal that both ESR signals are manifestations of the ubisemiquinone complex with the High-Potential Iron-Sulfur protein of succinate dehydrogenase.