1H NMR studies of 1-methylimidazole complex of cytochrome c

Abstract

Some hyperfine shifted 1H resonances of 1-methylimidazole complex of horse ferricytochrome c (1-MeIm·cyt c) have been assigned for the first time using 1D saturation transfer and 2D EXSY exchange correlated spectroscopy) experiments. Kinetic and equilibrium data for 1-MeIm binding to cyt c at a temperature range of 303–319 K have been determined at pH 7.0 by using the NMR method. The observed thermodynamic parameters for 1-MeIm binding are ΔH° = 39.5 kJ·mol −1, ΔS° = 154 J·mol −1·K −1, and Ea = 142 kJ·mol −1. The source of the asymmetric spin density distribution in heme groups of 1-MeIm·cyt c and the reason of low affinity of cytochrome c for 1-MeIm are also discussed.