Studies on the electron transport system. XLIII. The isolation of a succinic-coenzyme Q reductase from beef heart mitochondria

Abstract

The isolation of the succinic-CoQ reductase from beef heart mitochondria is described. The flavine content of the preparation is 4.8 mμmoles/mg. protein, and all of the flavine is extracted by acid only after the preparation is treated with proteolytic enzymes. The preparation also contains non-heme iron, lipid, and protoheme, and the last mentioned is present in an amount equivalent to the flavine. Based on the flavine or heme content, the minimum molecular weight in terms of protein is 210,000. The heme present in the purified enzyme is not reduced by succinate, which makes its participation as an electron carrier in the reactions catalyzed by the enzyme very unlikely. A rapid spectrophotometric method for measuring the succinic-CoQ reductase activity of mitochondria and of the purified enzyme is described.