1H NMR studies of azide binding to cytochrome c

The binding of azide ion to the heme iron of ferricytochrome c in D2O is studied using H-1 NMR methods at pH 7.0 and 300 K or 315 K. Some hyper-fine shifted resonances arising from heme peripheral protons and resonances of side-chain protons of some amino acid residues in N-3-cyt c have been assigned using 2D EXSY and DQF-COSY methods. The majority of the heme pocket side-chain proton signals have been identified. The 1D nuclear overhauser effect (NOE) difference spectra and 2D NOESY spectrum are presented and changes in NOE patterns between the heme and certain residues, and several residues around the axial ligand are interpreted in terms of changes in the pocket structure. Interpretation of NOE data indicates that conformation changes are obvious on the Met80 side of the heme cavity in the environment of the axial ligand in N-3-cyt c. In addition, kinetics analysis of azide binding to cpt c is studied using 2D EXSY method. (C) 1995 Elsevier Science B.V.