EPR detectable electron acceptors in submitochondrial particles from beef heart with special reference to the iron-sulfur components of DPNH-ubiquinone reductase

An attempt is made to identify and assign, for sonic fragments from beef heart mitochondria at various oxidation states, all electron magnetic resonances which have been resolved thus far at observation temperatures ≥4.2° K. Novel features of this work are the resolution of four different iron sulfur centers of the DPNH-ubiquinone reductase fragment and the observation of an unidentified electron acceptor — maximally evident at intermediate oxidation states — which is concentrated in the DPNH-cytochrome c reductase fraction.