13C and proton NMR studies of horse cytochrome c. Systematic assignment of methyl and methine resonances in both oxidation states.

The CHn groups in the aliphatic side chains of horse cytochrome c have been characterized according to the chemical shifts of both 13C-NMR and 1H-NMR signals, their temperature dependence and the number of attached protons, n. The primary assignments of resonances from the 55 side-chain methyl and the 27 methine groups were obtained directly for the oxidised and the reduced forms. Specific assignments of the 13C resonances were obtained through shift-correlation experiments and comparison with earlier 1H-NMR studies, by further measurements of proton-proton interactions, or by elimination. Comparison of the paramagnetic shifts of carbon and protons indicates a small redox-related change of conformation in the vicinity of Trp59 and a significant expansion of the protein over 30-50 degrees C.