<?xml version="1.0" encoding="UTF-8"?><xml><records><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>17</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Logunov, Stephan L.</style></author><author><style face="normal" font="default" size="100%">El-Sayed, Mostafa A</style></author><author><style face="normal" font="default" size="100%">Lanyi, Janos K.</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">Catalysis of the retinal subpicosecond photoisomerization process in acid purple bacteriorhodopsin and some bacteriorhodopsin mutants by chloride ions.</style></title><secondary-title><style face="normal" font="default" size="100%">Biophysical journal</style></secondary-title><alt-title><style face="normal" font="default" size="100%">Biophys. J.</style></alt-title></titles><keywords><keyword><style  face="normal" font="default" size="100%">Acoustics</style></keyword><keyword><style  face="normal" font="default" size="100%">Anions</style></keyword><keyword><style  face="normal" font="default" size="100%">Bacteriorhodopsins</style></keyword><keyword><style  face="normal" font="default" size="100%">Biophysical Phenomena</style></keyword><keyword><style  face="normal" font="default" size="100%">Biophysics</style></keyword><keyword><style  face="normal" font="default" size="100%">Catalysis</style></keyword><keyword><style  face="normal" font="default" size="100%">Chlorides</style></keyword><keyword><style  face="normal" font="default" size="100%">Halobacterium salinarum</style></keyword><keyword><style  face="normal" font="default" size="100%">Hydrogen-Ion Concentration</style></keyword><keyword><style  face="normal" font="default" size="100%">Kinetics</style></keyword><keyword><style  face="normal" font="default" size="100%">Photochemistry</style></keyword><keyword><style  face="normal" font="default" size="100%">Point Mutation</style></keyword><keyword><style  face="normal" font="default" size="100%">Retinaldehyde</style></keyword><keyword><style  face="normal" font="default" size="100%">Spectrophotometry</style></keyword></keywords><dates><year><style  face="normal" font="default" size="100%">1996</style></year><pub-dates><date><style  face="normal" font="default" size="100%">1996 Sep</style></date></pub-dates></dates><volume><style face="normal" font="default" size="100%">71</style></volume><pages><style face="normal" font="default" size="100%">1545-53</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">The dynamics and the spectra of the excited state of the retinal in bacteriorhodopsin (bR) and its K-intermediate at pH 0 was compared with that of bR and halorhodopsin at pH 6.5. The quantum yield of photoisomerization in acid purple bR was estimated to be at least 0.5. The change of pH from 6.5 to 2 causes a shift of the absorption maximum from 568 to 600 nm (acid blue bR) and decreases the rate of photoisomerization. A further decrease in pH from 2 to 0 shifts the absorption maximum back to 575 nm when HCl is used (acid purple bR). We found that the rate of photoisomerization increases when the pH decreases from 2 to 0. The effect of chloride anions on the dynamics of the retinal photoisomerization of acid bR (pH 2 and 0) and some mutants (D85N, D212N, and R82Q) was also studied. The addition of 1 M HCl (to make acid purple bR, pH 0) or 1 M NaCl to acid blue bR (pH 2) was found to catalyze the rate of the retinal photoisomerization process. Similarly, the addition of 1 M NaCl to the solution of some bR mutants that have a reduced rate of retinal photoisomerization (D85N, D212N, and R82Q) was found to catalyze the rate of their retinal photoisomerization process up to the value observed in wild-type bR. These results are explained by proposing that the bound Cl- compensates for the loss of the negative charges of the COO- groups of Asp85 and/or Asp212 either by neutralization at low pH or by residue replacement in D85N and D212N mutants.</style></abstract><issue><style face="normal" font="default" size="100%">3</style></issue><custom1><style face="normal" font="default" size="100%">http://www.ncbi.nlm.nih.gov/pubmed/8874028?dopt=Abstract</style></custom1><electronic-resource-num><style face="normal" font="default" size="100%">10.1016/S0006-3495(96)79357-8</style></electronic-resource-num></record><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>17</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Logunov, Stephan L.</style></author><author><style face="normal" font="default" size="100%">El-Sayed, Mostafa A</style></author><author><style face="normal" font="default" size="100%">Lanyi, Janos K.</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">Replacement effects of neutral amino acid residues of different molecular volumes in the retinal binding cavity of bacteriorhodopsin on the dynamics of its primary process.</style></title><secondary-title><style face="normal" font="default" size="100%">Biophysical journal</style></secondary-title><alt-title><style face="normal" font="default" size="100%">Biophys. J.</style></alt-title></titles><keywords><keyword><style  face="normal" font="default" size="100%">Bacteriorhodopsins</style></keyword><keyword><style  face="normal" font="default" size="100%">Binding Sites</style></keyword><keyword><style  face="normal" font="default" size="100%">Biophysical Phenomena</style></keyword><keyword><style  face="normal" font="default" size="100%">Biophysics</style></keyword><keyword><style  face="normal" font="default" size="100%">Halobacterium salinarum</style></keyword><keyword><style  face="normal" font="default" size="100%">Kinetics</style></keyword><keyword><style  face="normal" font="default" size="100%">Mutagenesis, Site-Directed</style></keyword><keyword><style  face="normal" font="default" size="100%">Photochemistry</style></keyword><keyword><style  face="normal" font="default" size="100%">Quantum Theory</style></keyword><keyword><style  face="normal" font="default" size="100%">Retinaldehyde</style></keyword><keyword><style  face="normal" font="default" size="100%">Schiff Bases</style></keyword></keywords><dates><year><style  face="normal" font="default" size="100%">1996</style></year><pub-dates><date><style  face="normal" font="default" size="100%">1996 Jun</style></date></pub-dates></dates><volume><style face="normal" font="default" size="100%">70</style></volume><pages><style face="normal" font="default" size="100%">2875-81</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">We have determined the rate and quantum yield of retinal photoisomerization, the spectra of the primary transients, and the energy stored in the K intermediate in the photocycle of some bacteriorhodopsin mutants (V49A, A53G, and W182F) in which residue replacements are found to change the Schiff base deprotonation kinetics (and thus the protein-retinal interaction). Because of their change in the local volume resulting from these individual replacements, these substitutions perturb the proton donor-acceptor relative orientation change and thus the Schiff base deprotonation kinetics. These replacements are thus expected to change the charge distribution around the retinal, which controls its photoisomerization dynamics. Subpicosecond transient spectroscopy as well as photoacoustic technique are used to determine the retinal photoisomerization rate, quantum yield, and the energy stored in the K-intermediate for these mutants. The results are compared with those obtained for wild-type bacteriorhodopsin and other mutants in which charged residues in the cavity are replaced by neutral ones. In some of the mutants the rate of photoisomerization is changed, but in none is the quantum yield or the energy stored in the K intermediate altered from that in the wild type. These results are discussed in terms of the shapes of the potential energy surfaces of the excited and ground states of retinal in the perpendicular configuration within the protein and the stabilization of the positive charge in the ground and the excited state of the electronic system of retinal.</style></abstract><issue><style face="normal" font="default" size="100%">6</style></issue><custom1><style face="normal" font="default" size="100%">http://www.ncbi.nlm.nih.gov/pubmed/8744325?dopt=Abstract</style></custom1><electronic-resource-num><style face="normal" font="default" size="100%">10.1016/S0006-3495(96)79857-0</style></electronic-resource-num></record><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>17</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Song, Li</style></author><author><style face="normal" font="default" size="100%">Logunov, Stephan L.</style></author><author><style face="normal" font="default" size="100%">Yang, Difei</style></author><author><style face="normal" font="default" size="100%">El-Sayed, Mostafa A</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">The pH dependence of the subpicosecond retinal photoisomerization process in bacteriorhodopsin: evidence for parallel photocycles.</style></title><secondary-title><style face="normal" font="default" size="100%">Biophysical journal</style></secondary-title><alt-title><style face="normal" font="default" size="100%">Biophys. J.</style></alt-title></titles><keywords><keyword><style  face="normal" font="default" size="100%">Bacteriorhodopsins</style></keyword><keyword><style  face="normal" font="default" size="100%">Biophysical Phenomena</style></keyword><keyword><style  face="normal" font="default" size="100%">Biophysics</style></keyword><keyword><style  face="normal" font="default" size="100%">Hydrogen-Ion Concentration</style></keyword><keyword><style  face="normal" font="default" size="100%">Isomerism</style></keyword><keyword><style  face="normal" font="default" size="100%">Kinetics</style></keyword><keyword><style  face="normal" font="default" size="100%">Molecular Structure</style></keyword><keyword><style  face="normal" font="default" size="100%">Photochemistry</style></keyword><keyword><style  face="normal" font="default" size="100%">Retinaldehyde</style></keyword></keywords><dates><year><style  face="normal" font="default" size="100%">1994</style></year><pub-dates><date><style  face="normal" font="default" size="100%">1994 Nov</style></date></pub-dates></dates><volume><style face="normal" font="default" size="100%">67</style></volume><pages><style face="normal" font="default" size="100%">2008-12</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">The pH dependence of the subpicosecond decay of the retinal photoexcited state in bacteriorhodopsin (bR) is determined in the pH range 6.8-11.3. A rapid change in the decay rate of the retinal photoexcited state is observed in the pH range 9-10, the same pH range in which a rapid change in the M412 formation kinetics was observed. This observation supports the previously proposed heterogeneity model in which parallel photocycles contribute to the observed pH dependence of the M412 formation kinetics in bR.</style></abstract><issue><style face="normal" font="default" size="100%">5</style></issue><custom1><style face="normal" font="default" size="100%">http://www.ncbi.nlm.nih.gov/pubmed/7858138?dopt=Abstract</style></custom1><electronic-resource-num><style face="normal" font="default" size="100%">10.1016/S0006-3495(94)80684-8</style></electronic-resource-num></record></records></xml>