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|Title:||Moessbauer Studies on Partially Oriented Samples of Carbon Monoxymyoglobin and Photodissociated Carbon Monoxymyoglobin|
|Author(s):||Emberson, Richard Maury, Jr.|
|Department / Program:||Physics|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Subject(s):||Physics, Condensed Matter|
|Abstract:||('57)Fe studies on partially oriented samples of carbon monoxy myoglobin (MbCO) and photodissociated carbon monoxy myoglobin (Mb*CO) are reported. The partial orientation was achieved by photodissociating MbCO utilizing the heme group's optical anisotropy, high quantum efficiency, and the slow recombination rate of Mb*CO at 4.2(DEGREES)K. The spectrum of each Mb species consists of a doublet which is the result of the quadrupole interaction with the electric field gradient (EFG) at the ('57)Fe nucleus. The photo-produced partial orientation affects the intensity ratio R of the two lines; measurements of R versus the fraction MbCO remaining allows the determination of the asymmetry parameter (eta) of the EFG and the angle (psi) between its principal axis V(,zz) and the normal to the optical axis, which coincides with the heme normal. The goal of this study was to demonstrate the feasibility of such an experiment by measuring (eta) and (psi) for MbCO and Mb*CO.
A theoretical model was developed which included corrections^arising from sample dichroism and anisotropy in the recoilless^fraction of the Mossbauer transition, and experiments verified the^functional dependence of R on the direction of the polarization (epsilon)(' )^and the fraction of MbCO remaining after flash off. For MbCO they^yield (psi) = 20 (+OR-) 5(DEGREES), (eta)= 0.2 (+OR-) 0.2. This value resolves an ambiguity^left by measurements on single crystals, which gave (psi) = 12(DEGREES) or 54(DEGREES),^(eta) = 0, since it is compatible with only the smaller value. For Mb*CO, which is spectroscopically almost identical with CO-free myoglobin, Mb, an angle (psi) = 57 (+OR-) 5(DEGREES) was found, which precludes a determination of (eta). It might be construed that this value indicates that of the two solutions of Mb single crystal experiments, (psi) = 39(DEGREES) and 68(DEGREES), (eta) = 0.7, (psi) = 68(DEGREES) is the correct one, but differences in the environment of the iron in Mb and Mb*CO can not be ruled out, since at 4.2(DEGREES)K the flashed-off CO remains trapped near the iron, and the molecule can not relax to the equilibrium conformation of Mb.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1981.
|Date Available in IDEALS:||2015-05-13|