Extended x-ray absorption fine structure of copper in cytochrome coxidase: Direct evidence for copper—sulfur ligation

The copper x-ray fluorescence excitation spectrum of cytochrome coxidase (ferrocytochrome c:oxygen oxidoreductase, EC 1.9.3.1) has been recorded in the 245—270 K range. The beat pattern observed in the extended x-ray absorption fine structure can be accounted for only by postulating a combination of sulfur and nitrogen (or oxygen) ligands to the copper. The average Cu—S distance is 2.27 ± 0.02 Å and the average Cu—N (or Cu—O) distance is 1.97 ± 0.02 Å. The amplitudes require ca, 1-1.5 sulfurs and 2 nitrogens (or oxygens) per copper. The distribution of sulfur ligands between CuAand CuBsites is not known, although there is some evidence that two sulfur atoms are bound to CuA.