Single crystals of bovine heart cytochrome c oxidase at fully oxidized resting, fully reduced and CO-bound fully reduced states are isomorphous with each other

Abstract

Fully reduced and CO-bound fully reduced forms of cytochrome c oxidase from beef heart muscle were crystallized in the presence of sodium ascorbate under N 2 or CO atmosphere. Hexagonal bipyramidal and tetragonal crystals were obtained for both forms depending on buffer species. The hexagonal bipyramidal crystals, as large as 0.6 mm in the largest dimension, diffracted X-rays at 7 Å resolution, showing an identical space group and cell dimension, P6 2 or P6 4 and a = b = 209 A ̊ , c = 283 A ̊ , respectively. These parameters coincide with those for crystals of the fully oxidized resting enzyme. This result suggests that a large conformational change, like a subunit arrangement, is not induced by the redox change and/or binding of CO (and possibly O 2) to heme a 3.