X-RAY-ABSORPTION SPECTROSCOPY OF ORIENTED CYTOCHROME-OXIDASE

The polarized X-ray absorption spectra of the copper, iron and zinc sites of mitochondrial cytochrome oxidase in oriented membrane multilayers have been examined. The copper X-ray absorption edge spectra indicate the presence of a tetragonal copper, which we assign as Cu(B), oriented with the long axis approximately orthogonal to the membrane normal. We have also detected the presence of a relatively long (2.6 angstrom) Cu-S or Cu-Cl interaction, which we assign to a copper-thioether (probably Met210) coordination at the Cu(A) site, with the bond oriented along the membrane normal. The coordination of the zinc, the iron and the Cu(B) heme a3 binuclear site are discussed.