title: Cytochrome oxidase (a3) heme and copper observed by low-temperature Fourier transform infrared spectroscopy of the CO complex.
abstract: Carbon monoxide bound to iron or copper in substrate-reduced mitochondrial cytochrome c oxidase (ferrocytochrome c:oxygen oxidoreductase, EC 1.9.3.1) from beef heart has been used to explore the structural interaction of the a3 heme-copper pocket at 15 K and 80 K in the dark and in the presence of visible light. The vibrational absorptions of CO measured by a Fourier transform infrared interferometer occur in the dark at 1963 cm-1, with small absorptions near 1952 cm-1, and are due to a3 heme--CO complexes. These disappear in strong visible light and are replaced by a major absorption at 2062 cm-1 and a minor one at 2043 cm-1 due to Cu--CO. Relaxation in the dark is rapid and quantitative at 210 K, but becomes negligible below 140 K. The multiple absorptions indicate structural heterogeneity of cytochrome oxidase in mitochondria. The Cu--CO absorptions (vCO) are similar to those in hemocyanin--CO complexes from molluscs (vCO - 2062 cm-1) and crustaceans (vCO = 2043 cm-1). The 2062 cm-1 Cu--CO absorption of cytochrome oxidase is split into two bands at 15 K. Analysis of spectral data suggest the presence of a very nonpolar heme--Cu pocket in which the heme-CO complex is highly ordered, but in which the Cu--CO complex is much more flexible, especially above 80 K. A function for these structures in oxygen reduction is proposed.
mesh_terms: D000818:Animals; D001665:Binding Sites; D002248:Carbon Monoxide / Q000378:metabolism*; D002417:Cattle; D003300:Copper / Q000378:metabolism; D003576:Electron Transport Complex IV / Q000378:metabolism; D005583:Fourier Analysis; D006418:Heme / Q000378:metabolism; D008929:Mitochondria, Heart; D013055:Spectrophotometry, Infrared
chemical_list: D006418:Heme; D003300:Copper; D002248:Carbon Monoxide; D003576:Electron Transport Complex IV