An iron sulfur protein in the mitochondrial outer membrane,reducible by NADH and NADPH

On addition of NADH or NADPH to the mitochondrial outer membrane fraction from rat liver, an electron paramagnetic resonance (EPR) spectrum is observed which is characteristic of a protein, containing an iron-sulfur center. The g-values are 2.01, 1.94 and 1.89. Quantitation of the EPR absorption and analysis of the acid labile sulfur content suggest that the paramagnetic center contains two iron and two acid labile sulfur atoms. The concentration of the center in the outer membrane is about 0.5 nmoles/mg protein.