Campus Units
Chemistry
Document Type
Article
Publication Version
Published Version
Publication Date
4-1991
Journal or Book Title
Biochemistry
Volume
30
Issue
16
First Page
3975
Last Page
3987
DOI
10.1021/bi00230a025
Abstract
Ultrafast absorption spectroscopy is used to study heme-NO recombination at room temperature in aqueous buffer on time scales where the ligand cannot leave its cage environment. While a single barrier is observed for the cage recombination of NO with heme in the absence of globin, recombination in hemoglobin and myoglobin is nonexponential. Examination of hemoglobin with and without inositol hexaphosphate points to proximal constraints as important determinants of the geminate rebinding kinetics. Molecular dynamics simulations of myoglobin and heme-imidazole subsequent to ligand dissociation were used to investigate the transient behavior of the Fe-proximal histidine coordinate and its possible involvement in geminate recombination. The calculations, in the context of the absorption measurements, are used to formulate a distinction between nonexponential rebinding that results from multiple protein conformations (substates) present at equilibrium or from nonequilibrium relaxation of the protein triggered by a perturbation such as ligand dissociation. The importance of these two processes is expected to depend on the time scale of rebinding relative to equilibrium fluctuations and nonequilibrium relaxation. Since NO rebinding occurs on the picosecond time scale of the calculated myoglobin relaxation, a time-dependent barrier is likely to be an important factor in the observed nonexponential kinetics. The general implications of the present results for ligand binding in heme proteins and its time and temperature dependence are discussed. It appears likely that, at low temperatures, inhomogeneous protein populations play an important role and that as the temperature is raised, relaxation effects become significant as well.
Copyright Owner
American Chemical Society
Copyright Date
1991
Language
en
File Format
application/pdf
Recommended Citation
Petrich, Jacob W.; Lambry, J.-C.; Kuczera, K.; Karplus, M.; Poyart, C.; and Martin, J.-L., "Ligand binding and protein relaxation in heme proteins: a room temperature analysis of nitric oxide geminate recombination" (1991). Chemistry Publications. 803.
https://lib.dr.iastate.edu/chem_pubs/803
Comments
Reprinted (adapted) with permission from Biochemistry 30 (1991): 3975, doi: 10.1021/bi00230a025. Copyright 1991 American Chemical Society.