Moessbauer Studies of Exchange-Coupled Two-Iron Centers in Proteins (Hemerythrin, Uteroferrin, Epr)
Sage, James Timothy
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https://hdl.handle.net/2142/77397
Description
Title
Moessbauer Studies of Exchange-Coupled Two-Iron Centers in Proteins (Hemerythrin, Uteroferrin, Epr)
Author(s)
Sage, James Timothy
Issue Date
1986
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
Language
eng
Abstract
This thesis reports Mossbauer measurements on three derivatives of the oxygen-transport protein hemerythrin and on the oxidized and reduced forms of uteroferrin, a purple acid phosphatase isolated from porcine uterine fluid. Both proteins contain an exchange-coupled pair of iron atoms coordinated directly to amino acid side chains.
A model that takes account of both the exchange coupling and the zero-field splitting at each site is presented and used to describe the magnetic properties of the ground spin multiplet of a pair of coupled spins. One notable feature of the model is the fact that the g- and A-tensors of the coupled system may be quite anisotropic even if the corresponding single-site tensors are not.
The model is applied in several Kramers systems and explains some unusual observations. In reduced uteroferrin, unexpectedly large anisotropies in the hyperfine tensor at the ferric site are rationalized naturally and in a way consistent with the other mag- netic properties. Similar observations on a sulfide derivative of hemerythrin appear to be susceptible to the same sort of expla- nation, although the Mossbauer simulations are not as refined. An unusual EPR spectrum observed in a nitric oxide derivative of deoxyhemerythrin is also explicable in the spin-coupling model; the corresponding Mossbauer spectra are reported but have not been analyzed in detail.
Preliminary studies of some non-Kramers systems are also presented. The Mossbauer spectrum of an azide derivative of deoxyhemerythrin broadens in a small applied field, indicating the presence of a near degeneracy. The spectrum of oxidized utero- ferrin broadens as the temperature is raised, even in the absence of an applied field. No fully adequate explanation for the latter observation is apparent.
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