Direct observation of the methionine residues of cytochrome c by 13C nuclear magnetic resonance spectroscopy.
The two Cepsilon-methyl methionine groups in cytochrome c have been chemically enriched (45%) with 13C. Their 13C NMR signals have been monitored in both the oxidized and reduced states and under various solution conditions. Methionine residue 80 showed characteristic chemical shift positions for the reduced Fe(II) and cyano-Fe(III) forms. No signal for methionine 80 was observed in the oxidized Fe(III) form due to the paramagnetic effect of the iron atom to which it is bonded, but the position of the methionine 65 signal was shifted, indicating that it is sensitive to the change of oxidation state. Two well resolved signals were observed at pH 11 for the Fe(III) form but only one was resolved at pH 2, indicating that while methionine 80 is definitely displaced from the iron atom at alkaline pH, it may not be in acid conditions.
D003574:Cytochrome c Group; D009682:Magnetic Resonance Spectroscopy; D008715:Methionine; D010084:Oxidation-Reduction
D003574:Cytochrome c Group; D008715:Methionine