13C NMR signal detection of iron-bound cyanide ions in ferric cyanide complexes of heme proteins.

13CN ion appears to have the greatest potential to probe the heme environment of the ferric heme proteins; however, a resonance of the iron-bound (13)CN ion in ferric heme proteins has not yet been located. We show here the first detection of (13)C NMR signals of the iron-bound (13)CN for heme proteins and their model complexes in an unexpectedly large upfield region. This study demonstrates that the (13)C NMR signal of the iron-bound (13)CN is a sensitive probe to study the nature of the proximal ligand in ferric heme protein.