The effect of digitonin on the cytochrome c oxidase activity of plant mitochondria

Abstract

The cytochrome c oxidase activity" of suspensions of plant mitochondria is increased by incubating them with 20 mg of digitonin/ml for 30 seconds. Increases ranging from 2.8 times to 52 times were recorded with mitochondria isolated from various plant tissues. Cytochrome oxidase was measured spectrophotometrically. In manometric experiments, rather smaller increases in activity were found when quinol was used as reducing agent, but with p-phenylenediamine there was no increase at all. Treatment with digitonin was more effective than were various other chemical, physical and enzymic treatments. It is suggested that digitonin acts by dispersing lipid links between protein molecules in the mitochondria in such a way as to render cytochrome oxidase molecules more accessible to their exogenous substrate, reduced cytochrome c.