Thermally induced changes in reconstituted and membranous cytochrome c oxidase

Abstract

The Arrhenius plots of electron transport activity in cytochrome c oxidase reconstituted with well-defined phospholipids were shown to display a change in slope at 20-25.degree. C regardless of the chemical nature of the incorporated lipid. In native membranous cytochrome c oxidase, the discontinuity in Arrhenius activity plot occurred at 16-18.degree. C. These temperature breaks were found to correlate with changes in spin-label mobilities but not with the bulk lipid transition observed by differential scanning calorimetry. Temperature-dependent reciprocal equilibrium between the immobilized and fluid pools is demonstrated. The changes in kinetic and spin-label spectral characteristics in cytochrome c oxidase membranes are probably related to a lipid-protein interaction prompted by a thermally induced change in the physical state of the lipids that does not involve a gel to liquid crystalline transition.