Theory of 14N and 17O Nuclear Quadrupole Interactions in the Single Amino Acids Occurring in the Protein Chain of Cytochrome c

R. H. Scheicher a, D. Cammarere a,b,  N. Sahoo a,c, K. Nagamine d,e and T. P. Das a *

a  Department of Physics, State University of New York at Albany, Albany, NY, 12222, USA
b  Tamarac High School, Brittenkill, NY, USA
c  Department of Radiation Oncology, Albany Medical College, Albany NY, 12208, USA
d  Muon Science Laboratory, RIKEN (The Institute of Physical and Chemical Research), Wako, Saitama 351-0198, Japan
e  Meson Science Laboratory, High Energy Accelerator Research Organization, Tsukuba,Ibaraki 305-0801, Japan

*  Corresponding Author: FAX 1-518-442-5260

In the last two years, the positive Muon (m) and Muonium (Mu) which can be considered as light protons and hydrogen atoms respectively have been used to study the nature of electron transport in proteins, the first system studied being the protein chain in Cytochrome c [1,2]. The idea behind the technique involved is that a m in the process of its implantation in the protein can capture an electron and become a Mu which in turn can get trapped by forming a covalent bond with an atom in the protein, like for instance oxygen. The Mu can then lose its electron by ionization and the electron moving away from the m left behind can cause spin-lattice relaxation effects for the m through the effect of the time-dependent perturbation associated with the fluctuating magnetic field arising from the moving electron. The observed relaxation of the m through the muon spin rotation (mSR) technique [3] then provides information on the nature of the motion of the electron involving one-, two- or three-dimensional pathways [1]. In trying to verify the premise of this experimental analysis involving trapping of the Mu, and also m at the same site as the Mu, after the electron has moved away, we have studied, through the Hartree-Fock Cluster procedure [4], the trapping of m and Mu at various sites in the individual amino acids such as for instance, Cysteine, Glycine, Alanine and Lysine through energy optimization. We have found [5] that the only site in each amino acid at which both the Mu and the m left behind can be trapped is the oxygen atom in the C=O group common to all amino acids.
For these studies, we have obtained the electronic structures of all the individual amino acids in Cytochrome c and the corresponding electronic structures with m and Mu trapped at the oxygen of the C=O group. We shall present results for the electric quadrupole coupling constants (e2qQ) and asymmetry parameters (m) [6] for the bare amino acids and the amino acids with trapped m and Mu. The trends in e2qQ and h for 17O and 14N between the various amino acids, as well as the changes in these parameters in the presence of m and Mu will be analyzed. Comparison will be made with available data for the bare systems. It is also hoped that extensions of the mSR technique will be able to provide experimental data in e2qQ and h for the 17O and 14N nuclei to compare with our predictions.

[1]  K. Nagamine et al., Physica B 289-290, 631 (2000).
[2]  K. Nagamine et al., RIKEN Revs. 20, 51 (1999).
[3]  A. Schenck, “Muon Spin Rotation Spectroscopy”, Adam Hilger Ltd., Bristol and Boston (1985).
[4]  See for instance T. P. Das in “Electronic Properties of Solids Using Cluster Methods”, T.A. Kaplan and S. D. Mahanti ed., Plenum Press, New York (1995), p. 1.
[5]  D. Cammarere et al., Physica B 289-290, 636 (2000).
[6]  T. P. Das and E. L. Hahn, “Nuclear Quadrupole Resonance Spectroscopy”, Academic Press Inc., New York (1958).

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