Affiliations: Graduate School of Materials Science, Nara Institute of Science and Technology, Ikoma, Nara 630‐0101, Japan
Note: [] Corresponding author: Dr. Mikio Kataoka, Department of Materials Science, Nara Institute of Science and Technology, Ikoma, Nara 630‐0101, Japan. Tel.: +81 743 72 6100; Fax: +81 743 72 6109; E‐mail: kataoka@ms.aist‐nara.ac.jp.
Abstract: Photoactive yellow protein (PYP) is a photoreceptor protein for the negative phototaxis of Ectothiorhodospira halophila. The crystal structures of several photo‐intermediates have been revealed by X‐ray crystallography. In the crystal structure of the active intermediate, PYPM, no significant structural changes were observed except for the vicinity of the chromophore. On the contrary, spectroscopic studies with solution condition demonstrated that global structural changes occur during the photo‐cycle. In order to reveal the origin of the discrepancies, we measured the reaction kinetics upon illumination under crystal condition and to compare them with those observed under solution condition. The reactive portion decreases with the increase of crystallinity. The rate constant of PYPM decay also decreases with the increase of crystallinity. These results suggest two possibilities: (1) PYP in crystal does not react by the illumination; (2) the photoreaction rate is highly accelerated in crystal. Consequently, the photoreaction in crystal is considered to be highly influenced by the force constraint from crystalline lattice.
Journal: Spectroscopy, vol. 17, no. 2-3, pp. 345-353, 2003
