FTIR studies of environmental effects on carbonmonoxymyoglobin
Hong, Mi Kyung
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https://hdl.handle.net/2142/23938
Description
Title
FTIR studies of environmental effects on carbonmonoxymyoglobin
Author(s)
Hong, Mi Kyung
Issue Date
1989
Doctoral Committee Chair(s)
Frauenfelder, Hans
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Fourier Transform Infrared Spectroscopy (FTIR)
carbonmonoxymyoglobin
myoglobin
protein-ligand systems
Language
en
Abstract
"In this thesis, Fourier Transform Infrared Spectroscopy (FTIR) was used to study
the interaction between the protein myoglobin (Mb), and substrate carbon-monoxide (CO),
as a model system of control in protein-ligand systems. IR spectra of the CO molecule
bound to Mb have been obtained as a function of intensive variables such as temperature,
pressure and pH, as well as in different solvents, and at low hydration. In addition, IR
spectra have been obtained for a genetically synthesized version of Mb with glycine
substituted for the distal histidine (His E7).
The IR spectra of CO bound to Mb consists of four bands labelled Ao. A 1· A 2 and
A3. The recombination rate of CO toMb following flash photolysis is different for each
band. Control may therefore be exercised at the binding site by changing the relative
populations of the bands. It is found that the primary effect of varying the above
mentioned thermodynamic variables from their physiological conditions, and of the genetic
substitution, is to increase the intensity of Ao at the expense of A 1· It is proposed that the
net effect of all these very different perturbations is to disrupt the hydrogen bonds in Mb.
This affects the protein on at least two different scales; first, a local scale, in which a
specific amino aci9-s residue is affected, altering the binding of CO to Mb through a steric
interaction, and second, a global scale, in which hydrogen bonds are disrupted in the bulk
of the protein structure, causing a slight change in the conformation of the protein as a
whole. This connection between local and global sources of control may be of general
significance to protein-ligand systems. It is also found that the temperature dependence of
the relative populations of the A states deviates from a Boltzman distribution called the
""ankle"" can be understood as a temperature-dependent entropy. This also shows that
protein has a similar behavior of a glass-forming liquid above the glass temperature."
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