title: Photoinduced volume change and energy storage associated with the early transformations of the photoactive yellow protein from Ectothiorhodospira halophila.
abstract: The photocycle of the photoactive yellow protein (PYP) isolated from Ectothiorhodospira halophila was analyzed by flash photolysis with absorption detection at low excitation photon densities and by temperature-dependent laser-induced optoacoustic spectroscopy (LIOAS). The quantum yield for the bleaching recovery of PYP, assumed to be identical to that for the phototransformation of PYP (pG), to the red-shifted intermediate, pR, was phi R = 0.35 +/- 0.05, much lower than the value of 0.64 reported in the literature. With this value and the LIOAS data, an energy content for pR of 120 kJ/mol was obtained, approximately 50% lower than for excited pG. Concomitant with the photochemical process, a volume contraction of 14 ml/photoconverted mol was observed, comparable with the contraction (11 ml/mol) determined for the bacteriorhodopsin monomer. The contraction in both cases is interpreted to arise from a protein reorganization around a phototransformed chromophore with a dipole moment different from that of the initial state. The deviations from linearity of the LIOAS data at photon densities > 0.3 photons per molecule are explained by absorption by pG and pR during the laser pulse duration (i.e., a four-level system, pG, pR, and their respective excited states). The data can be fitted either by a simple saturation process or by a photochromic equilibrium between pG and pR, similar to that established between the parent chromoprotein and the first intermediate(s) in other biological photoreceptors. This nonlinearity has important consequences for the interpretation of the data obtained from in vitro studies with powerful lasers.
authors.affiliation: Department of Microbiology, E. C. Slater Institute, University of Amsterdam, The Netherlands.
authors.forename: M E
authors.initials: ME
authors.lastname: van Brederode
authors.forename: T
authors.initials: T
authors.lastname: Gensch
authors.forename: W D
authors.initials: WD
authors.lastname: Hoff
authors.forename: K J
authors.initials: KJ
authors.lastname: Hellingwerf
authors.forename: S E
authors.initials: SE
authors.lastname: Braslavsky
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry*; D055592:Biophysical Phenomena; D001703:Biophysics; D002841:Chromatiaceae / Q000737:chemistry*; D007834:Lasers; D018499:Linear Energy Transfer; D008956:Models, Chemical; D010777:Photochemistry; D010782:Photolysis; D020283:Photoreceptors, Microbial; D013053:Spectrophotometry
chemical_list: D001426:Bacterial Proteins; D020283:Photoreceptors, Microbial; C050162:photoactive yellow protein, Bacteria