Absorption spectra of photoactive yellow protein chromophores in vacuum

¹ University of Aarhus
² Paris-Sud University

^* To whom correspondence should be addressed. E-mail: lha{at}phys.au.dk.

Submitted on February 25, 2005
Revised on April 19, 2005
Accepted on 17 June 2005

	Abstract

The absorption spectra of two photoactive yellow protein (PYP) model chromophores have been measured in vacuum using an electrostatic ion storage ring. The absorption spectrum of the isolated chromophore is an important reference for deducing the influence of the protein environment on the electronic energy levels of the chromophore, and separating the intrinsic properties of the chromophore from properties induced by the protein environment. In vacuum the deprotonated trans-thiophenyl-p-coumarate model chromophore has an absorption maximum at 460 nm, whereas PYP absorbs maximally at 446 nm. The protein environment thus only slightly blue-shifts the absorption. In contrast, the absorption of the model chromophore in aqueous solution is significantly blue-shifted (_max = 393 nm). A deprotonated trans-p-coumaric acid has also been studied to elucidate the effect of thioester formation and phenol deprotonation. The sum of these two changes on the chromophore induces a red-shift both in vacuum and in aqueous solution.

Key Words: PYP, coumaric acid, electronic spectroscopy, electrostatic storage ring, gas phase, photosensor

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