The transmembrane protein complex cytochrome c oxidase (CcO) is associated with the last step of the respiratory electron-transport system and catalyzes the reduction of oxygen to water. This enzyme of the heme-copper oxidase superfamily has been known to exist in either a slow or fast form with differing abilities to bind oxygen and other ligands. However, intricate structural details differentiating these two forms remained mostly unknown.

Now, Inez Weidinger and coworkers report experimental and theoretical studies characterizing the two forms of the CcO complex (DOI: 10.1021/jacs.0c10767). The scientists demonstrated that a Raman marker associated with ligands coordinating with the binuclear metal center within CcO is sensitive to the complex's slow and fast forms. They performed surface-enhanced Raman spectroscopy that discriminated against changes in the two states due to the potential at an enzyme-modified electrode. This study correlates spectral details from structural differences within the binuclear center of CcO and the proposed active form of residues involved in the electron-transport to oxygen. The authors conclude their work by demonstrating that the frequency differential between the two forms of the complex depends on a single tyrosine residue's protonation state in the enzyme's binuclear center.

Kruse et.al. (2021) A Resonance Raman Marker Band Characterizes the Slow and Fast Form of Cytochrome c Oxidase. J. Am. Chem. Soc. https://doi.org/10.1021/jacs.0c10767