The electron-transferring flavoprotein as a common intermediate in the mitochondrial oxidation of butyryl coenzyme A and sarcosine.

Butyryl coenzyme A dehydrogenase and a transfer protein required for maximal activity as measured by reduction of 2,6-dichloroindophenol have been solubilized from monkey (Macaca mulatta) liver mitochondria by sonic irradiation. The dehydrogenase has been purified approximately 60-fold and identified as a flavin adenine dinucleotide-specific flavoprotein. The required protein has been found to be indistinguishable from the electron-transferring flavoprotein (transfer protein) of the sarcosine dehydrogenase pathway as measured by extent of solubilization, manner of precipitation with ammonium sulfate, and adsorption on and elution from diethylaminoethyl cellulose. Purified preparations of transfer protein, measured at 450 mp, were reduced by catalytic amounts of butyryl dehydrogenase and sarcosine dehydrogenase with each enzyme causing approximately one-half of the total reduction. It is concluded that the transfer protein requirement for the oxidation of butyryl coenzyme A is met by the FAD-specific electron-transferring flavoprotein. The oxidation of radiosarcosine, in the presence of limiting amounts of transfer protein, has been shown to be inhibited 10 to 15% by reduced but not by oxidized butyryl dehydrogenase. Simultaneous measurements of 2,6-dichloroindophenol reduction have shown the combined rates of the two dehydrogenase-catalyzed reductions to be greater than the rate of the faster of the individual reactions. Purified transfer protein has been shown to be inactivated by heat treatment, yielding different curves for activity against temperature of inactivation for each activity monitoring dehydrogenase. Presently available evidence suggests that the mitochondrial oxidations of butyryl coenzyme A and of sarcosine are both mediated by a common electron-transferring flavoprotein.