Purification and properties of a new coupling factor required for oxidative phosphorylation in silicotungstate-treated submitochondrial particles.

It has been shown previously (1) that submitochondrial particles exposed to sonic oscillation at an alkaline pH and then treated with 1% silicotungstate were depleted of several coupling factors (F1,l Fz, Fs, and F5) as well as succinate dehydrogenase. Succinoxidase activity in these STA-particles was negligible but could be completely restored by addition of partially purified succinate dehydrogenase (2). The unexpected observation in these studies (1) was that the coupling factors and succinate dehydrogenase were not only required for oxidative phosphorylation with succinate as substrate but also with DPNH. Similarly, all five protein preparations were required to obtain maximal 32Pi-ATP exchange activity. In this paper data are presented to show that the stimulatory effect of the succinate dehydrogenase preparation on energy transfer is due to another protein component present in the preparation. This protein is distinct from previously reported coupling factors. It has been purified and partially characterized.