<?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%">Zhang, K</style></author><author><style face="normal" font="default" size="100%">Song, Li</style></author><author><style face="normal" font="default" size="100%">Dong, J</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%">Studies of cation binding in ZnCl2-regenerated bacteriorhodopsin by x-ray absorption fine structures: effects of removing water molecules and adding Cl- 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%">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%">Cations</style></keyword><keyword><style  face="normal" font="default" size="100%">Chlorides</style></keyword><keyword><style  face="normal" font="default" size="100%">Kinetics</style></keyword><keyword><style  face="normal" font="default" size="100%">Ligands</style></keyword><keyword><style  face="normal" font="default" size="100%">Spectrum Analysis</style></keyword><keyword><style  face="normal" font="default" size="100%">Water</style></keyword><keyword><style  face="normal" font="default" size="100%">X-Rays</style></keyword><keyword><style  face="normal" font="default" size="100%">Zinc</style></keyword><keyword><style  face="normal" font="default" size="100%">Zinc Compounds</style></keyword></keywords><dates><year><style  face="normal" font="default" size="100%">1997</style></year><pub-dates><date><style  face="normal" font="default" size="100%">1997 Oct</style></date></pub-dates></dates><volume><style face="normal" font="default" size="100%">73</style></volume><pages><style face="normal" font="default" size="100%">2097-105</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">The binding of Zn2+ in Zn2+-regenerated bacteriorhodopsin (bR) was studied under various conditions by x-ray absorption fine structures (XAFS). The 0.9:1 and 2:1 Zn2+:bR samples gave similar XAFS spectra, suggesting that Zn2+ might have only one strong binding site in bR. It was found that in aqueous bR solution, Zn2+ has an average of six oxygen or nitrogen ligands. Upon drying, two ligands are lost, suggesting the existence of two weakly bound water ligands near the cation-binding site in bacteriorhodopsin. When excess Cl- ions were present before drying in the Zn2+-regenerated bR samples, it was found that two of the ligands were replaced by Cl- ions in the dried film, whereas two remain unchanged. The above observations suggest that Zn2+ has three types of ligands in regenerated bR (referred to as types I, II, and III). Type I ligands are strongly bound. These ligands cannot be removed by drying or by exchanging with Cl- ions. Type II ligands cannot be removed by drying, but can be replaced by Cl- ligands. Type III ligands are weakly bound to the metal cation and are most likely water molecules that can be removed by evaporation under vacuum or by drying with anhydrous CaSO4. The results are discussed in terms of the possible structure of the strongly binding site of Zn2+ in bR.</style></abstract><issue><style face="normal" font="default" size="100%">4</style></issue><custom1><style face="normal" font="default" size="100%">http://www.ncbi.nlm.nih.gov/pubmed/9336205?dopt=Abstract</style></custom1><electronic-resource-num><style face="normal" font="default" size="100%">10.1016/S0006-3495(97)78240-7</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%">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></records></xml>