Succinic dehydrogenase sulfhydryl groups

NADH cytochrome c reductase was isolated from pigeon breast and pig heart muscle. The enzyme was shown to contain four atoms of iron per flavin molecule. NADH cytochrome c reductase, like succinic dehydrogenase, is a ferroflavoprotein. The ratio of iron to flavin is four. The enzyme contains sulfhydryl groups that can be titrated by classical methods, but their oxidation has no effect on the enzymatic activity. In contrast, the removal of the metal leads to a decrease in the ability of the enzyme to reduce cytochrome c. As for succinic dehydrogenase, the structure of the flavin in NADH cytochrome c reductase is not clear. It was demonstrated that it is not flavin mononucleotide, but the identity of the flavin component with flavin adenine dinucleotide is not established in fact, the flavin component differs from the classical FAD by its chromatographic properties and its behavior in enzymic assays. It is not known if it is a structural variation of the flavin nucleotide or if the nucleotide is conjugated to a peptide. 

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