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Dynamics and structure in the Mn 2+ site of concanavalin A as determined by high‐field EPR and ENDOR spectroscopy
Author(s) -
Goldfarb Daniella,
Narasimhulu Kuppala V.,
Carmieli Raanan
Publication year - 2005
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1668
Subject(s) - chemistry , electron paramagnetic resonance , hyperfine structure , electron nuclear double resonance , spectral line , crystallography , quadrupole , nuclear magnetic resonance , spectroscopy , pulsed epr , zero field splitting , analytical chemistry (journal) , electron , atomic physics , spin echo , medicine , physics , astronomy , quantum mechanics , radiology , chromatography , magnetic resonance imaging , spin polarization
The properties of the Mn 2+ site in the protein concanavalin A were investigated by single crystal W‐band EPR/ENDOR (electron‐nuclear double resonance) measurements. Initially, room temperature EPR measurements were carried out, one type of Mn 2+ was identified and its zero‐field splitting (ZFS) tensor was determined. In contrast, low temperature EPR measurements showed that two chemically inequivalent Mn 2+ are present, Mn A 2+ and Mn B 2+ , differing in their ZFS tensors. Variable temperature measurements revealed a two‐site exchange between the two types. Although the dynamic process has been characterized by its rate and activation energy, just from the EPR measurements it was not possible to assign it to a specific residue. 1 H ENDOR measurements of the water and imidazole protons, which are the main contributors to the ENDOR spectra, showed only one type of signals, namely, they were not sensitive to the differences between Mn A 2+ and Mn B 2+ . 55 Mn ENDOR spectra, which are dominated by the 55 Mn isotropic hyperfine, a iso , and the nuclear quadrupole interaction did sense the differences. Analysis of the spectra recorded with the magnetic field along the crystallographic axes showed that the two have the same a iso but different quadrupole tensors. Copyright © 2005 John Wiley & Sons, Ltd.