Respiratory chain succinate:quinone oxidoreductases (or Complex II)

• Cecilia Hägerhäll

Complex II or succinate:quinone oxidoreductase is an enzyme complex located at the heart of metabolism, since it is a member of both the citric acid cycle and the respiratory chain. The classical Complex II found f.ex. in mammals, consist of four proteins, a flavoprotein containing covalently bound FAD, and iron-sulfur protein with three FeS clusters, and two membrane-spanning polypeptides that contain one heme group. However, several variations on this conserved theme exist (for a review see Biochim. Biophys. Acta 1320:107-141)

The figure depicts the homologous enzyme, quinol:fumarate reductase from Wolinella succinogenes that was crystallized by Roy Lancasters group in Frankfurt. The figure is drawn using the coordinates of PDB 1QLA.

We have a long standing interest in the membrane anchor of Complex II, and particularly those enzymes that contain two hemegroups.  In collaboration with Lo Gortons group at Dept of Analytical Chemistry, we have initiated bioelectrochemical studies of intact diheme Complex II interacting with an electrode surface. These studies have resulted in new insights about the functional mechanism of the cytochrome, descibed in an upcoming publication.