Conformational relaxation in heme proteins: Ligand rebinding above the glass transition

Below the glass-transition temperature of the solvent, heme proteins are frozen into static conformations, and ligand rebinding is well described with a time- and temperature-independent distribution of enthalpic barriers, $g(H)$. This work addresses the relaxation of the enthalpic barriers that sets in near the glass transition of the solvent as significant protein motions occur on the time scale of rebinding. As the heme domes fully toward its equilibrium deoxy structure, the distribution of enthalpies changes with time and temperature. A simple phenomenological model is used to describe MbCO rebinding at all temperatures above 50 K. Like the glassy relaxations observed in MbCO upon a sudden pressure release, the relaxation of all barriers to higher enthalpy is nonexponential in time and does not obey an Arrhenius relation. The extent of the enthalpic shift is consistent with a prediction based upon the inhomogeneous rebinding of band III, the charge transfer band observed in unligated Mb near 13100 cm$\sp{-1}$. Geminate rebinding from 160 to 290 K is well described in MbCO by a relaxation of all barriers by 9.3 kJ/mol without invoking any wells along the reaction coordinate representing ligand migration into the protein matrix. A simple argument is used to estimate the rate coefficient for ligand escape into the solvent. It, too, is found to have a non-Arrhenius temperature dependence.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Physics

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2011

Author dc:creator

• Steinbach, Peter John

Contributors dc:contributor

• Frauenfelder, Hans

• Biophysics, General

Statement dc:rights

• Copyright 1990 Steinbach, Peter John

Language dc:language

eng

Identifier

AAI9114423
(UMI)AAI9114423

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/22953