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

AbstractWe 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 a3. These changes may play an important role in all studies that involve flash photolysis of cytochrome c oxidase-ligand complexes