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https://hdl.handle.net/2142/23877
Description
Title
Motions in myoglobin
Author(s)
Johnson, Jeffrey Bruce
Issue Date
1991
Doctoral Committee Chair(s)
Frauenfelder, Hans
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
myoglobin
protein motions
ligand binding
pressure release
flash photolysis
Language
en
Abstract
"When the structure of myoglobin was first revealed by x-ray crystallography, it was discovered
that there was no clear evidence of a pathway for ligands to enter the protein to bind at the
heme iron. Motions within the protein are necessary for the protein to function. Pressure release
and flash photolysis experiments help characterize some of these protein motions.
Sperm whale carbonmonoxymyoglobin exhibits three spectroscopically distinguishable carbon
monoxide stretch bands between 1910 cm-1 and 1990 cm-1 labeled A0 , Ah and A3 . Pressure
release measurements reveal three relaxations in the protein which are measured by: (1)
the shifting in frequency of Ao, and the exchanges (2) A1 --+ A3, and (3) Ao --+ A1 + A3. Each
relaxation is non-Arrhenius and solvent viscosity dependent.
The rebinding of the A substates was observed after flash photolysis by monitoring the
Soret band and the A substates. The low-temperature rebinding (20K-160K) exhibit increasing
rebinding rates with increasing temperature. The three A substates show different rebinding
rates. From ""' 170K to ""' 220K, the rebinding rate decreases with increasing temperature in
each A substate. Between 220K and ""' 300K, the absorbance change of Ao is non-monotonic in
time due to an interconversion between Ao and A1 + A3 during rebinding. This interconversion
rate matches well with the extrapolated interconversion rate deduced from pressure release
measurements. Since the three A substates have different rebinding rates, it is possible that the
binding process is controlled in part by the interconversion between A substates.
The maximum entropy method applied to the rebinding data reveals five peaks in the distribution
of rebinding rates, labeled (from fast to slow) 1,2,3,E, and S. Peak 1 is due to geminate
rebinding. Peaks 2 and 3 are well characterized, but not well understood. Peak 2 is present in all
the A substates (except possibly A3 ) with the same rate as peak 2 monitored in the Soret. Peak
3 is the same in the Soret, A1 and likely A3 , however, it is absent in Ao. Peak 3 matches closely
with the extrapolated interconversion between A1 and A3 and the shifting of peak frequency of
Ao measured in pressure release experiments. PeakE is due to the interconversion Ao --+ A 1 + A3
and peak S arises from the rebinding of CO from the solvent."
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