Open AccessPerturbations of the distal heme pocket in human myoglobin mutants probed by infrared spectroscopy of bound CO: correlation with ligand binding kinetics.
Author(s) -
Sriram Balasubramanian,
David G. Lambright,
Steven G. Boxer
Publication year - 1993
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.90.10.4718
Subject(s) - myoglobin , chemistry , kinetics , steric effects , heme , mutant , hemeprotein , ligand (biochemistry) , infrared spectroscopy , crystallography , infrared , biophysics , stereochemistry , biochemistry , enzyme , biology , receptor , physics , organic chemistry , quantum mechanics , optics , gene
The infrared spectra of CO bound to human myoglobin and myoglobin mutants at positions His-64, Val-68, Asp-60, and Lys-45 on the distal side have been measured between 100 and 300 K. Large differences are observed with mutations at His-64 and Val-68 as well as with temperature and pH. Although distal His-64 is found to affect CO bonding, Val-68 also plays a major role. The variations are analyzed qualitatively in terms of a simple model involving steric interaction between the bound CO and the distal residues. A strong correlation is found between the final barrier height to CO recombination and the CO stretch frequency: as compared to wild type, the barrier is smaller in those mutants that have a higher CO stretch frequency (vCO) and vice versa. Possible reasons for this correlation are discussed. It is emphasized that the temperature and pH dependence of both the kinetics and the infrared spectra must be measured to obtain a consistent picture.