Carbon-13 nuclear magnetic resonance of heme carbonyls. Cytochrome c and carboxymethyl derivatives of cytochrome c

Abstract
Carbonyl complexes of horse heart cytochrome c and various carboxymethylated derivatives were examined using 13C NMR spectroscopy. The multiplicity and chemical shift of the 13CO resonance were functions of pH and the extent of alkylation. Correlations were made among prominent features of the chemical shift titration curves and changes in the environment of the heme. A simple model compatible with the bulk of previous observations was suggested to account for the several carbonyl resonance peaks and the complex behavior of the chemical shift with changes in pH.