Cytochrome c oxidase in plant mitochondria

Abstract

Rebinding of CO after flash photolysis of the carboxy mixed-valence cytochrome c oxidase in plant mitochondria has been monitored in the visible range at low temperature (160-210K). At 586/630 nm, the photodissociation of the CO-saturated suspension was followed by a largely incomplete rebinding of CO to Fea3. After a series of three to four flashes, the unbound species accumulated up to 85% of the total enzyme, the remaining 15% CO-bound form undergoing recombination repetitively. In the Soret region, the absorbance level after the first flash came back to the initial one, as if all the CO-bound form were restored. However, the amount of complex which could be photodissociated by a second flash was only part of the starting material, in agreement with observations in the alpha range. The unbound species exhibited optical features very similar to the ones of compound C. The lack of CO rebinding is interpreted as due to an electron redistribution induced by the flash photolysis. This electron transfer has been tentatively assigned to a concomitant CuB oxidation and CuA reduction on the basis of the 655 nm band as a probe for a3+3 [Beinert et al. (1976) Biochim. Biophys. Acta 423, 339-355] and of the optical features in the visible range. Results are discussed with respect to analogous investigations with beef heart mitochondria and the studies by Boelens and Wever (1979-1982) of electron transfer after photolysis of the carboxy mixed-valence state when using the isolated mammalian enzyme at room temperature.