Light-induced structural changes in cytochrome c oxidase : Measurements of electrogenic events and absorbance changes

Abstract

We have investigated flash-induced electrogenic events and absorbance changes in cytochrome c oxidase in the absence of dioxygen and carbon monoxide. Electrogenic events were studied using a Teflon-bound layer of cytochrome c oxidase oriented in a phospholipid monolayer. Absorbance changes were observed exclusively in partly reduced cytochrome c oxidase; the largest changes were found in the one-electron-reduced species. Electrogenic events were detected in all reduction states of the enzyme. Both types of experiments displayed a rapid (< 0.5 μ;s) event followed by a biphasic relaxation. The time constants of the relaxation were 6 ± 2 μ;s and 70 ± 10 μ;s in the electrogenicity, and 9 ± 3 μ;s and 81 ± 6 μ;s in the absorbance changes (at ~22 °C). The kinetic absorbance difference spectrum was consistent with that of reduced minus oxidized haem. The experimental results are discussed in terms of structural changes in the vicinity of cytochrome a 3. These changes may play an important role in all studies that involve flash photolysis of cytochrome c oxidase-ligand complexes.