Studies on succinic dehydrogenase. V. Isolation and properties of the dehydrogenase from baker's yeast

1. 1. The succinic dehydrogenase of baker's yeast has been solubilized and isolated from the particulate fraction of the cell wherein the enzyme is localized. The best preparations obtained were 65 % pure by ultracentrifugal analysis. 2. 2. The enzyme is an amber-brown protein, containing 4 atoms of iron and 1 mole of flavine per mole of protein. No method has been found to remove either the iron or the flavine without denaturation of the protein. The iron was readily liberated in the inorganic form by acid or thermal denaturation, but separation of the flavine from the protein required extensive proteolytic digestion of the latter. The flavine, set free in this manner, was not free FAD but, like that from the beef heart enzyme, appeared to be in bound form, possibly as peptide derivatives. 3. 3. The action of the enzyme is readily reversible. Inactivation on aging usually entailed a much greater loss of succinic dehydrogenase than of fumaric reductase activity. 4. 4. The following aspects of the action of the enzyme have been studied: effects of pH and temperature; specificity for electron carriers; inhibition by sulfhydryl reagents and iron complexors; kinetic constants for succinate, malonate, and fumarate; and turnover number. 5. 5. In most respects the yeast enzyme resembles closely its counterpart in beef heart mitochondria.