Electron Paramagnetic Resonance and Electron Spin Echo Studies of Co 2+ Coordination by Nicotinamide Adenine Dinucleotid
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Appl Magn Reson (2013) 44:817–826 DOI 10.1007/s00723-013-0444-z
Magnetic Resonance
Electron Paramagnetic Resonance and Electron Spin Echo Studies of Co2+ Coordination by Nicotinamide Adenine Dinucleotide (NAD+) in Water Solution Stanisław K. Hoffmann • Janina Goslar Stefan Lijewski
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Received: 14 November 2012 / Revised: 31 January 2013 / Published online: 24 February 2013 Ó The Author(s) 2013. This article is published with open access at Springerlink.com
Abstract Co2? binding to the nicotinamide adenine dinucleotide (NAD?) molecule in water solution was studied by electron paramagnetic resonance (EPR) and electron spin echo at low temperatures. Cobalt is coordinated by NAD? when the metal is in excess only, but even in such conditions, the Co/NAD? complexes coexist with Co(H2O)6 complexes. EPR spin-Hamiltonian parameters of the Co/NAD? complex at 6 K are gz = 2.01, gx = 2.38, gy = 3.06, Az = 94 9 10-4 cm-1, Ax = 33 9 10-4 cm-1 and Ay = 71 9 10-4 cm-1. They indicate the low-spin Co2? configuration with S = 1/2. Electron spin echo envelope modulation spectroscopy with Fourier transform of the modulated spin echo decay shows a strong coordination by nitrogen atoms and excludes the coordination by phosphate and/or amide groups. Thus, Co2? ion is coordinated in pseudo-tetrahedral geometry by four nitrogen atoms of adenine rings of two NAD? molecules.
1 Introduction Nicotinamide adenine dinucleotide (NAD?) molecule consists of two nucleotides joined by two bridging phosphate groups. The nucleotides consist of ribose rings with one nucleotide containing adenosine base and the other containing nicotinamide (Fig. 1). NAD? plays several essential roles in metabolism of living organisms where it appears as b-diastereomer. It acts as a coenzyme in redox reactions of cellular respiration and is involved in an intermolecular electron transfer. NAD? is a donor of ADP ribosylation reaction and acts as a substrate for bacterial DNA ligases [1]. NAD? is very flexible molecule with over a dozen rotatable bonds that can adopt a wide variety of environmentally dependent S. K. Hoffmann (&) J. Goslar S. Lijewski Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17, 60-179 Poznan, Poland e-mail: [email protected]; [email protected]
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conformations [2, 3]. The two extreme NAD? conformations are a folded and an extended configuration. The folded (compact) conformer (Fig. 1a), having aromatic rings in close proximity, exists in water solutions where it reduces solvation accessible molecular surface area. The folded conformation also appears in a single crystal of nicotinamide adenine dinucleotide tetrahydrate both at room [4] and at low temperature (100 K) [5] and is stabilized by hydrogen bonds to the crystalline water molecules. NAD? bound to enzyme adopts an extended (open) conformation (Fig. 1b) allowing a catalytic activity by forming weak hydrogen bonds between an enzyme and the cofactor [6, 7]. Extended configuration is preferred for a free NAD
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