The Physical Environment and Oxidative and Phosphorylative Capacities of Higher Plant Mitochondria

Abstract

The effect of the tonicity of the ambient solution during the preparation of mitochondrial suspensions was studied with respect to the succinoxidase, malic oxidase, and a -ketoglutaric oxidase activity of mitochondria from cauliflower buds (Brassica oleracea). In the presence of soluble protoplast components hypotonicity proved injurious in all cases, injury increasing markedly with temp. When particles were freed of other protoplast components, succinoxidase activity was subsequently little affected by exposure of particles to a large vol. (30 ml.) of distilled water, whereas the activity of malic and a -ketoglutaric oxidase was seriously impaired. The use of dilute salt solutions (10-3 M KC1, for example) precluded the injury elicited by distilled water, as did suspension of particles in small vols. (2.0 ml.) of distilled water. Tonicity in the manometer flask detd. final oxidase activity. Succinoxidase exhibited considerably higher tonic requirements than malic oxidase for maximal activity. Phosphorylation accompanying succinate oxidation was completely abolished by hypotonic treatment of the particles regardless of the suspending vol. or the presence of neutral salt The phosphorylations accompanying malic and [alpha] -ketoglutaric oxidase activity were approximately as sensitive to hypotonicity as the oxidase activity, and equally responsive to salt treatment.