Cytochrome a(3) structure in bovine cytochrome oxidase.

The iron-carbon monoxide stretching mode and the iron-carbon- oxygen bending mode in CO cytochrome oxidase have been assigned at 520 and 578 cm(-2), respectively. The frequencies, widths, and intensities of these modes show that the Fe-C-O grouping in CO cytochrome a(3) is linear but significantly tilted from the normal to the home plane. These data can account for the binding affinities of CO and O2 under physiological conditions.