Four quinone reduction sites in the NADH dehydrogenase complex

Abstract

Quinones can be used as electron acceptors and donors in a new approach to the study and resolution of the respiratory chain-linked NADH dehydrogenase system of beef heart mitochondria. Juglone (5-hydroxynapthoquinone), ubiquinone, duroquinone (tetramethylbenzoquinone), and ferricyanide are found to react at four separate sites in the complex. The sites can be defined by chemical and enzymatic inhibition or by fractionation of the system. The reduced form of one quinone, duroquinol, has the unique property of being an electron donor for the energy-linked reduction of NAD +.