Abstract
A protein factor, designated as Factor B, was extracted from lyophilized acetone-washed bovine heart mitochondria and purified by ammonium sulfate fractionation, and ion-exchange chromatography on DEAE-cellulose and CM-cellulose. Centrifugation in a sucrose density gradient showed that the activity of the purified factor was closely associated with a symmetrical protein peak comprising approximately 70% of the protein. Its molecular weight was estimated to be 32,000, using hemoglobin and cytochrome c as markers. Factor B produces several-fold stimulation of ATP-driven NAD reduction, and of net phosphorylation coupled to NADH or succinate oxidation in ammonia particles. The stimulation of ATP-driven NAD reduction activity exceeds that given by an optimal amount of oligomycin, and in the presence of a saturation level of Factor B, oligomycin stimulation disappears. Also, Factor B stimulation is evident in urea-depleted particles which have been supplemented by Factor A. These particles show no stimulation by oligomycin. The results suggest that Factor B may participate in the energy transfer reactions between the respiratory chain and the terminal step resulting in ATP synthesis.
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