The effect of pH on proton transport by bacteriorhodopsin |
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| Affiliation: | 1. Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, Vavilov St. 32, 119991, Moscow, Russia;2. I.M. Sechenov First Moscow State Medical University, Ministry of Healthcare of the Russian Federation, Trubetskaya St. 8/2, 119991, Moscow, Russia;3. Faculty of Biology, Lomonosov Moscow State University, Leninskie Gory, 1/12, Moscow, 119234, Russia;4. Moscow Institute of Physics and Technology, 141700, Dolgoprudnyi, Moscow Region, Russia;1. Graduate Program in Materials Science, Universidade Federal Do Vale Do São Francisco, Juazeiro, BA, 48920-310, Brazil;2. Departamento de Física, Universidade Federal de Pernambuco, Av. Prof. Moraes Rego, 1235, Cidade Universitária, Recife, PE, 50670-901, Brazil;3. Departamento de Ciencias Físicas, Universidad de La Frontera, Temuco, Chile;4. Departamento de Ingeniería Mecánica, Universidad de La Frontera, Temuco, Chile;1. Department of Pharmacy, University of Naples “Federico II”, via Mezzocannone 16, 80134 Napoli, Italy;2. Interuniversity Research Centre on Bioactive Peptides (CIRPeB), via Mezzocannone 16, 80134 Napoli, Italy;3. Institute of Biostructure and Bioimaging (IBB), CNR, via Mezzocannone 16, 80134 Napoli, Italy;4. Institute of Crystallography (IC), CNR, Via Amendola 122, 70126 Bari, Italy;1. Department of Chemistry, University of Konstanz, 78457 Konstanz, Germany;2. Institute for Biophysical Chemistry, Goethe-University Frankfurt, 60438 Frankfurt am Main, Germany |
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| Abstract: | The pH-dependence of proton motion during the photocycle was investigated by measuring the photoelectric signals due to charge displacement inside bacteriorhodopsin molecules. Measurements were performed on purple membranes oriented in suspension and the kinetics of flash excited electric and light absorption signals was compared. It was found that in the pH range 4.5–8 the photocycle and the successive proton movements have identical kinetics, and do not depend on pH. In the pH range 8–10 both kinetics change, though differently; the charge motion decouples from the photocycle and the photocycle seems to split up into two parallel paths, the photoelectric signal becomes faster. However, the net proton transfer remains the same as at lower pH values. Above pH ≈ 10, the photocycle behaves differently and cannot be described by the parallel pathway model and the net proton displacement drops. The results are explained by the successive titration of two groups (probably tyrosine) participating in proton translocation. |
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