title: Modeling the membrane potential generation of bacteriorhodopsin.
abstract: The archaeon Halobacterium salinarum can grow phototrophically with only light as its energy source. It uses the retinal containing and light-driven proton pump bacteriorhodopsin to enhance the membrane potential which drives the ATP synthase. Therefore, a model of the membrane potential generation of bacteriorhodopsin is of central importance to the development of a mathematical model of the bioenergetics of H. salinarum. To measure the current produced by bacteriorhodopsin at different light intensities and clamped voltages, we expressed the gene in Xenopus laevis oocytes. We present current-voltage measurements and a mathematical model of the current-voltage relationship of bacteriorhodopsin and its generation of the membrane potential. The model consists of three intermediate states, the BR, L, and M states, and comparisons between model predictions and experimental data show that the L to M reaction must be inhibited by the membrane potential. The model is not able to fit the current-voltage measurements when only the M to BR phase is membrane potential dependent, while it is able to do so when either only the L to M reaction or both reactions (L to M and M to BR) are membrane potential dependent. We also show that a decay term is necessary for modeling the rate of change of the membrane potential.
authors.affiliation: Max Planck Institute of Biochemistry, Department of Membrane Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany.
authors.forename: Ricardo C H
authors.initials: RC
authors.lastname: del Rosario
authors.forename: Christoph
authors.initials: C
authors.lastname: Oppawsky
authors.forename: Jörg
authors.initials: J
authors.lastname: Tittor
authors.forename: Dieter
authors.initials: D
authors.lastname: Oesterhelt
mesh_terms: D000818:Animals; D001436:Bacteriorhodopsins / Q000235:genetics / Q000502:physiology*; D005260:Female; D019617:Halobacterium salinarum / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology*; D008954:Models, Biological; D018408:Patch-Clamp Techniques; D014162:Transfection; D014982:Xenopus laevis
chemical_list: D001436:Bacteriorhodopsins