A 1H NMR NOE study on Co(II) stellacyanin: some clues about the structure of the metal site.

The 1H NMR spectrum of Co(II) stellacyanin is reported, in which four signals not previously observed have been detected. NOE experiments were performed to assign the hyperfine shifted signals corresponding to a Cys and two His residues. Both His residues are solvent-accessible and are shown to bind the metal ion through their N delta 1 atoms. The beta-CH2 Cys proton shifts indicate the presence of a strong axial ligand.