Relationship between lateral diffusion, collision frequency, and electron transfer of mitochondrial inner membrane oxidation-reduction components.

Abstract

Fluorescence recovery after photobleaching was used to determine the diffusion coefficients of the oxidation-reduction (redox) components ubiquinone, complex III (cytochromes b-c1), cytochrome c and complex IV (cytochrome oxidase) of the [rat liver] mitochondrial inner membrane. All redox components diffuse in 2 dimensions as common-pool electron carriers. Cytochrome c diffuses in 2 and 3 dimensions concomitantly, and its diffusion rate, unlike that of all other redox components, is modulated along with its activity by ionic strength. The diffusion coefficients established reveal that the theoretical diffusion-controlled collision frequencies of all redox components are greater than their experimental maximum (uncoupled) turnover numbers. Since electron transport is slower than the theoretical limit set by the lateral diffusion of the redox components, ordered chains, assemblies or aggregates of redox components are not necessary to account for electron transport. Mitochondrial electron transport is diffusion coupled, consistent with a random-collison model for electron transport.