Involvement of a dithiol protein in mitochondrial energy-linked functions and its relation to coupling factor B.

The coupling factor protein isolated previously in pure form with a molecular weight of 11–12 × 10³ (K.-S. You and Y. Hatefi, 1976, Biochim. Biophys. Acta423, 398–412) has been shown to restore ATP-induced NAD reduction by succinate, transhydrogenation from NADH to NADP, and ATP-³³P_i exchange to submitochondrial particles rendered deficient by extraction with 1 m NH₄OH. The factor also stimulated the oxidative phosphorylation activity of the extracted particles 2.5- to >3-fold. The stimulatory effect of the factor was inhibited by mercurials, Cd²⁺, phenylarsine oxide, and diamide, indicating that it contains an essential dithiol. Dithiothreitol and dihydrolipoate did not replace the protein factor in stimulating the deficient particles. The purified dithiol-containing protein was precipitated and inhibited by antibody raised against coupling factor B. Since this antibody also inhibits coupling factor F₂, it is concluded that the active principle of coupling factors B and F₂ is the purified dithiol-containing protein of molecular weight 11–12 × 10³ referred to above.