High-pressure near-infrared Raman spectroscopy of bacteriorhodopsin light to dark adaptation.
Near-infrared (NIR) Raman spectroscopy is employed as an in situ probe of the chromophore conformation to study the light to dark-adaptation process in bacteriorhodopsin (bR) at variable pressure and temperature in the absence of undesired photoreactions. In dark-adapted bR deconvolution of the ethylenic mode into bands assigned to the all-trans (1526 cm-1) and 13-cis (1534 cm-1) isomers yields a 13-cis to all-trans ratio equal to 1 at ambient pressure (Schulte et al., 1995, Appl. Spectrosc. 49:80-83). Detailed spectroscopic evidence is presented that at high pressure the equilibrium is shifted toward the 13-cis isomers and that the light to dark adaptation kinetics is accelerated. The change in isomeric composition with temperature and pressure as well as the kinetics support a two-state model activation volumes of -16 ml/mol for the transition of 13-cis to all-trans and -22 ml/mol for the reverse process. These compare with a conformational volume difference of 6.6 ml/mol, which may be attributed to the ionization of one or two residues or the formation of three hydrogen bonds.
Schulte
A
A
Department of Physics, University of Central Florida, Orlando 32816-2385, USA.
Bradley
L
L
D001436:Bacteriorhodopsins / Q000737:chemistry* / Q000378:metabolism* / Q000528:radiation effects; D003624:Darkness; D019617:Halobacterium salinarum / Q000378:metabolism; D007259:Infrared Rays; D007700:Kinetics; D008027:Light; D011312:Pressure; D011487:Protein Conformation; D013059:Spectrum Analysis, Raman / Q000295:instrumentation / Q000379:methods; D013816:Thermodynamics; D013997:Time Factors
D001436:Bacteriorhodopsins