title: Effect of high pressure on the absorption spectrum and isomeric composition of bacteriorhodopsin.
abstract: The effects of high pressure upon the absorption spectra and isomeric composition of the dark (bRD) and light adapted (bRL) forms of bacteriorhodopsin were examined. Pressure favors the 13-cis form of bacteriorhodopsin (bR13-cis). The equilibrium isomeric composition and absorption spectra of bacteriorhodopsin samples at a given pressure were the same starting from either light or dark adapted bacteriorhodopsin. From the effect of pressure on the equilibrium constant between bRall-trans in equilibrium bR13-cis in the dark, the molar volume change between bRall-trans and bR13-cis was found to be -7.8 +/- 3.2 ml/mol. This volume change suggests a difference in conformation between dark- and light-adapted bacteriorhodopsin, but the magnitude of the change is small, involving only a small number of the protein residues.
mesh_terms: D001436:Bacteriorhodopsins; D002338:Carotenoids; D055598:Chemical Phenomena; D002621:Chemistry; D003624:Darkness; D006217:Halobacterium; D008027:Light; D011312:Pressure; D013053:Spectrophotometry
chemical_list: D002338:Carotenoids; D001436:Bacteriorhodopsins