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Author  |
Weber, S.; Biskup, T.; Okafuji, A.; Marino, A.R.; Berthold, T.; Link, G.; Hitomi, K.; Getzoff, E.D.; Schleicher, E.; Norris, J.R.J. |
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Title |
Origin of light-induced spin-correlated radical pairs in cryptochrome |
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Journal Article |
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Year |
2010 |
Publication |
The Journal of Physical Chemistry. B |
Abbreviated Journal |
J Phys Chem B |
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Volume |
114 |
Issue |
45 |
Pages |
14745-14754 |
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Keywords |
Animals; Cryptochromes/*chemistry/*metabolism; Electron Spin Resonance Spectroscopy; Electron Transport/radiation effects; Flavin-Adenine Dinucleotide/metabolism; Free Radicals/chemistry/metabolism; *Light; Models, Molecular; Protein Conformation; Xenopus Proteins/chemistry/metabolism; Xenopus laevis |
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Abstract |
Blue-light excitation of cryptochromes and homologues uniformly triggers electron transfer (ET) from the protein surface to the flavin adenine dinucleotide (FAD) cofactor. A cascade of three conserved tryptophan residues has been considered to be critically involved in this photoreaction. If the FAD is initially in its fully oxidized (diamagnetic) redox state, light-induced ET via the tryptophan triad generates a series of short-lived spin-correlated radical pairs comprising an FAD radical and a tryptophan radical. Coupled doublet-pair species of this type have been proposed as the basis, for example, of a biological magnetic compass in migratory birds, and were found critical for some cryptochrome functions in vivo. In this contribution, a cryptochrome-like protein (CRYD) derived from Xenopus laevis has been examined as a representative system. The terminal radical-pair state FAD(*)...W324(*) of X. laevis CRYD has been characterized in detail by time-resolved electron-paramagnetic resonance (TREPR) at X-band microwave frequency (9.68 GHz) and magnetic fields around 345 mT, and at Q-band (34.08 GHz) at around 1215 mT. Different precursor states, singlet versus triplet, of radical-pair formation have been considered in spectral simulations of the experimental electron-spin polarized TREPR signals. Conclusively, we present evidence for a singlet-state precursor of FAD(*)...W324(*) radical-pair generation because at both magnetic fields, where radical pairs were studied by TREPR, net-zero electron-spin polarization has been detected. Neither a spin-polarized triplet precursor nor a triplet at thermal equilibrium can explain such an electron-spin polarization. It turns out that a two-microwave-frequency TREPR approach is essential to draw conclusions on the nature of the precursor electronic states in light-induced spin-correlated radical pair formations. |
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Address |
Institute of Physical Chemistry, Albert-Ludwigs-Universitat Freiburg, 79104 Freiburg, Germany. Stefan.Weber@physchem.uni-freiburg.de |
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English |
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ISSN |
1520-5207 |
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Notes |
PMID:20684534 |
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Call Number |
IT'IS @ evaj @ |
Serial |
259 |
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