Intermediates generated during the reaction of reduced Rhodobacter sphaeroides cytochrome c oxidase with dioxygen

Cytochrome oxidase is one of the functionally most intriguing redox-driven proton pumps. During the last decade our increased understanding of the system has greatly benefited from theoretical calculations and modeling in the framework of three-dimensional structures of cytochrome c oxidases from different species. Because these studies are based on results from experiments, it is important that any ambiguities in the conclusions extracted from these experiments are discussed and elucidated. In a recent study Szundi et al. (Szundi et al. Biochemistry 2012, 51, 9302) investigated the reaction of the reduced Rhodobacter sphaeroides cytochrome c oxidase with O₂ and arrived at conclusions different from those derived from earlier investigations. In this short communication we compare these very recent data to those obtained from earlier studies and discuss the origin of the differences.