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Updated: Aug 15, 2026

Structure and Coordination Determination of Peptide-metal Complexes Using 1D and 2D 1H NMR
Published on: December 16, 2013
Dynamics and structure in the Mn2+ site of concanavalin A as determined by high-field EPR and ENDOR spectroscopy
Daniella Goldfarb1, Kuppala V Narasimhulu, Raanan Carmieli
1Departments of Chemical Physics, The Weizmann Institute of Science, Rehovot, Israel 76100. daniella.goldfarb@weizmann.ac.il
Abstract:
The properties of the Mn2+ 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 Mn2+ was identified and its zero-field splitting (ZFS) tensor was determined. In contrast, low temperature EPR measurements showed that two chemically inequivalent Mn2+ 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. 1H 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+. 55Mn ENDOR spectra, which are dominated by the 55Mn 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.
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