Isolation and Enzymatic Properties of the Mitochondrial Reduced Diphosphopyridine Nucleotide Dehydrogenase

Abstract

Abstract The DPNH dehydrogenase of the mitochondrial electron transport system has been obtained in a highly purified, soluble form after resolution of DPNH-coenzyme Q reductase (Complex I) particles by chaotropic agents. The enzyme contains 1 mole of flavin mononucleotide, 4 g atoms of iron, and 4 moles of acid-labile sulfide per 70,000 g. The soluble, but not the particle-bound, enzyme behaves as a diaphorase and catalyzes the unspecific reduction of quinones and ferric compounds such as menadione, 2,6-dichloroindophenol, coenzymes Q, ferricyanide, and cytochrome c. Mercurials inhibit all the reductase activities of the soluble dehydrogenase, and DPNH (g10-4 m) inhibits its menadione and coenzyme Q reductase activities. The structure and function of DPNH dehydrogenase in both the soluble and the particle-bound form are discussed.