The gas-phase absorption spectrum of a neutral GFP model chromophore
Lutz Lammich 1, Michael Axman 2, Mogens Brøndsted Nielsen 2 and Lars H Andersen 1*
1 Univ. of Aarhus
2 Univ. of Copenhagen
* To whom correspondence should be addressed. E-mail: lha{at}phys.au.dk.
Submitted on July 20, 2006
Revised on September 18, 2006
Accepted on 19 September 2006
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Abstract |
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We have studied the gas-phase absorption properties of the Green Fluorescent Protein (GFP) chromophore in its neutral (protonated) charge state in a heavy-ion storage ring. To accomplish this we synthesized a new molecular chromophore with a charged NH3 group attached to a neutral model chromophore of GFP. The gas-phase absorption cross section of this chromophore molecule as a function of the wavelength is compared to the well known absorption profile of GFP. The chromophore has a maximum absorption at 415±5 nm. When corrected for the presence of the charged group attached to the GFP model chromophore the unperturbed neutral chromophore is predicted to have an absorption maximum at 399 nm in vacuum. This is very close to the corresponding absorption peak of the protein at 397 nm. Together with previous data obtained with an anionic GFP model chromophore the present data show that the absorption of GFP is primarily determined by intrinsic chromophore properties. In other words there is strong experimental evidence that in terms of absorption the conditions in the hydrophobic interior of this protein are very close to those in vacuum.
Key Words:
GFP, chromophore, electronic spectroscopy, electrostatic storage ring, gas phase
