PROTON-RESONANCE ASSIGNMENTS AND LIGAND-EXCHANGE KINETICS IN HIGH-SPIN AND MIXED-SPIN MYOGLOBIN COMPLEXES USING 2-DIMENSIONAL EXCHANGE SPECTROSCOPY

The task of assigning resonances in proton nuclear magnetic resonance spectra of paramagnetic heme proteins can be an arduous process, but w ith the development of multi-dimensional NMR methods the situation has improved. It is demonstrated here that two-dimensional exchange spect roscopic experiments can be used to obtain to assignment correlations for the heme protons of methydroxy-, metthiocyano-, metaquo-, and meti midazole-myoglobin forms. All the assignments are unambiguous and stra ightforward when the temperature and mixing times are adjusted to mini mize nuclear Overhauser cross-peaks from each complex. Moreover, satur ation transfer experiments allow the study of ligand binding kinetics. The exchange rates between metaquo- and metimidazole- (or methyl subs tituted imidazole) myoglobin complexes are estimated. The differences between the exchange rates reflect differences in the hydrophobic and steric interactions between the ligands and the protein moiety. (C) 19 98 Elsevier Science B.V. All rights reserved.