Hydrogen Atoms Are Produced When Tryptophan within a Protein Is Irradiated with Ultraviolet Light |
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Authors: | Paul J Angiolillo Jane M Vanderkooi |
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Institution: | The Johnson Research Foundation, Department of Biochemistry and Biophysics, University of Pennsylvania, Philadelphia, PA, USA |
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Abstract: | Abstract— The UV photolysis of the aromatic amino acid, tryptophan (Trp), in the Ca2+-binding protein, cod paralbumin, type III, was studied using electron paramagnetic resonance (EPR) spectroscopy in the temperature range 4–80 K. For the Ca2+-bound protein, irradiation with UV light (250–400 nm) resulted in the generation of atomic hydrogen with a hyperfine splitting of 50.9 mT, whereas in the Ca2+-free form, where the Trp is exposed to solvent, the trapped atomic hydrogen was not in evidence. In the same spectra, the radical signal in the g = 2.00 region could be detected. The line shape of the Ca2+-bound form is similar to the EPR line shape obtained for Trp in micellar systems. In contrast, the EPR line shape for the Ca2+-free form is essentially featureless up to 80 K. The EPR spectra of the photoproducts of Trp and the nature of the photoreactions are therefore sensitive to the environment of Trp within the protein. |
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