Resolution and reconstitution of complex II (succinate-ubiquinone reductase) by salts

Abstract

The effects of representative chaotropic ions (NO 3 −, ClO 4 −, Cl 3CCOO −) on the resolution, and antichaotropic ions (SO 4 −2, HPO 4 −, F −) on the reconstitution of a water-insoluble multiprotein-lipid complex (succinate-ubiquinone reductase or complex II) have been studied. Succinate dehydrogenase appears to be bound to the components of the complex mainly by hydrophobic attractions. This association is considerably stronger when the complex is suspended in D 2O rather than in H 2O. The resolution of complex II with respect to succinate dehydrogenase is an equilibrium process. The equilibrium can be shifted in the direction of resolution by chaotropic salts, and in the direction of reconstitution of complex II either by removal of the added chaotrope or by addition of an antichaotropic salt. The chaotrope-induced resolution of complex II has a small but significant temperature dependence. As might be expected, the equilibrium of a partially resolved complex II system can be shifted in either direction by altering the temperature of the medium. Similar to complexes I and III, the reduced form of complex II appears to be more stable to resolution than its oxidized form.