Electron nuclear double resonance of cytochrome oxidase: nitrogen and proton ENDOR from the 'copper' EPR signal.

Proton ENDOR resonances have been found from at least two different protons with fairly large and isotropic couplings of about 12 and 19 MHz. It is possible that such protons are attached to carbons that are one bond removed from the point of ligation to copper. A number of weakly coupled protons with anisotropic couplings have also been seen. None of the protons, either weakly or strongly coupled, appears to exchange with 2H2O. We have obtained nitrogen ENDOR from at least one nitrogen with a hyperfine coupling large enough for the nitrogen to be a ligand of copper. We have not yet demonstrated experimentally ENDOR characteristic of the copper nucleus itself.