On reagents that convert cytochrome oxidase from an inactive to an active coupling state.

Cytochrome oxidase (ferrocytochrome c:oxygen oxidoreductase, EC 1.9.3.1) of beef heart mitochondria, prepared by a standard method and brought to the highest purity level, is essentially inactive when tested in the aerobic assay involving oxidation of reduced cytochrome c by molecular oxygen. Three reagents (lysolecithin, Tween 20, and exogenous phospholipids) can convert cytochrome oxidase from an inactive to an active coupling state. These conversions are reversible: i.e., removal of the inducing agent leads to loss of activity. The evidence for the intrinsic coupling capability is that cytochrome oxidase in the active state invariably generates a proton gradient during respiration, and such gradient formation is demonstrable even when cytochrome oxidase is not inserted into a liposome.