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https://hdl.handle.net/2142/20973
Description
Title
Relaxation dynamics in heme proteins
Author(s)
Scholl, Reinhard Wilhelm
Issue Date
1991
Doctoral Committee Chair(s)
Frauenfelder, Hans
Department of Study
Physics
Discipline
Physics
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Physics, Molecular
Biophysics, General
Language
eng
Abstract
A protein molecule possesses many conformational substates that are likely arranged in a hierarchy consisting of a number of tiers. A hierarchical organization of conformational substates is expected to give rise to a multitude of nonequilibrium relaxation phenomena. If the temperature is lowered, transitions between substates of higher tiers are frozen out, and relaxation processes characteristic of lower tiers will dominate the observational time scale.
This thesis addresses the following questions: (i) What is the energy landscape of a protein? How does the landscape depend on the environment such as pH and viscosity, and how can it be connected to specific structural parts? (ii) What relaxation phenomena can be observed in a protein? Which are protein specific, and which occur in other proteins? How does the environment influence relaxations? (iii) What functional form best describes relaxation functions? (iv) Can we connect the motions to specific structural parts of the protein molecule, and are these motions important for the function of the protein?
To this purpose, relaxation processes after a pressure change are studied in carbonmonoxy (CO) heme proteins (myoglobin-CO, substrate-bound and substrate-free cytochrome P450cam-CO, chloroperoxidase-CO, horseradish peroxidase-CO) between 150 K and 250 K using FTIR spectroscopy to monitor the CO bound to the heme iron. Two types of p-relaxation experiments are performed: p-release (200 $\to$ $\simeq$40 MPa) and p-jump ($\simeq$40 $\to$ 200 MPa) experiments.
Most of the relaxations fall into one of three groups and are characterized by (i) nonexponential time dependence and non-Arrhenius temperature dependence (FIM1($\nu$), FIM1($\Gamma$)); (ii) exponential time dependence and non-Arrhenius temperature dependence (FIM0(A$\sb{i}\to$ A$\sb{j}$)); exponential time dependence and Arrhenius temperature dependence (FIMX($\nu$)).
The influence of pH is studied in myoglobin-CO and shown to have a strong influence on the substate population of the highest tier, tier 0, but not on the relaxation rates. Two different viscosities in myoglobin-CO are compared. The dependence of relaxations on the thermodynamic history of a sample is shown. For substrate-free P450cam-CO, relaxations after a p-jump are observed far above the glass transition of the protein-solvent system.
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