AN ENDOR AND ESEEM STUDY OF THE BLUE COPPER PROTEIN AZURIN

We report electron-nuclear double-resonance experiments on a single cr ystal of azurin at 95 GHz and electron-spin-echo envelope-modulation e xperiments on frozen solutions of azurin and of the H117G mutant at 9 GHz. The hyperfine and quadrupole tensors of the two remote nitrogens of the histidine ligands of copper are assigned and discussed. A third nucleus is found to contribute to the echo-modulation spectrum and th is probably concerns an amide nitrogen of the peptide backbone.