Photoreaction Cycle of Photoactive Yellow Protein from Ectothiorhodospira halophila Studied by Low-Temperature Spectroscopy
- 1 January 1996
- journal article
- research article
- Published by American Chemical Society (ACS) in Biochemistry
- Vol. 35 (45), 14047-14053
- https://doi.org/10.1021/bi961342d
Abstract
The photocycle of photoactive yellow protein (PYP) from Ectothiorhodospira halophila was studied by low-temperature spectroscopy. Irradiation of PYP at −190 °C produced a photo-steady-state mixture composed of bathochromic and hypsochromic photoproducts (PYPB and PYPH). Upon warming, PYPH was thermally converted to a slightly blue-shifted intermediate (PYPHL) above −150 °C and then to a red-shifted one (PYPL) above −80 °C. PYPB was thermally converted to the blue-shifted intermediate (PYPBL) above −180 °C and then to PYPL above −90 °C. PYPL thermally reverted to PYP above −50 °C, completing the photocycle. The spectral properties of PYPL formed at low temperature suggest that it corresponds to the red-shifted photoproduct detected in the nano- to microsecond time scale at room temperature (A465). The absolute absorption spectra of PYPH, PYPB, and PYPL were estimated, and their absorption maxima were determined to be 442 and 489 nm at −190 °C and 456 nm at −80 °C, respectively. Although a near-UV intermediate (A355) is observed in the recovery process of PYP from A465 at room temperature, it was not detected at low temperatures, probably due to the effects of temperature and the presence of glycerol. A scheme of the photocycle of PYP is presented.Keywords
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