Two-Photon-Absorption of Bacteriorhodopsin: Formation of a Red-shifted Thermally Stable Photoproduct F620
Thorsten Fischer 1 and Norbert A Hampp 2*
1 Univ. of Marburg
2 University of Marburg
* To whom correspondence should be addressed. E-mail: hampp{at}staff.uni-marburg.de.
Submitted on November 8, 2004
Revised on December 16, 2004
Accepted on 6 May 2005
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Abstract |
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By means of high intensity 532 nm laser pulses a photochemical conversion of the initial B570 state of bacteriorhodopsin (BR) to a stable photoproduct absorbing maximally at about 620 nm in BR suspensions and at about 610 nm in BR films is induced. This state, which we named F620, is photochemically further converted to a group of three products with maximal absorptions in the wavelength range from 340 nm to 380 nm, which show identical spectral properties to the so-called P360 state reported in the literature. The photoconversion from B570 to F620 is most likely a resonant two-photon absorption induced step. The formation of F620 and P360 leads to a distinguished photo-induced permanent optical anisotropy in BR films. The spectral dependence of the photo-induced anisotropy and the anisotropy orientations at the educt (B570) and product (F620) wavelengths are strong indicators that F620 is formed in a direct photochemical step from B570. The chemical nature of the P360 products probably is that of a retro-retinal containing BR, but the structural characteristics of the F620 state are still unclear. The photo-induced permanent anisotropy induced by short laser pulses in BR films helps both to better understand the photochemical pathways related to this transition as well as it is interesting in view of potential applications as this feature is the molecular basis for permanent optical data storage using BR films.
Key Words:
bacteriorhodopsin, bacteriorhodopsin films, laser-induced-blue-membrane, optical anisotropy, purple memebrane, two-photon-absorption
