BACTERIORHODOPSIN AS A MODEL FOR PROTON PUMPS

According to a long-standing hypothesis, membrane pumps function by fl ip-flopping between two protein conformations that allow alternative a ccess of the ion binding site to the two membrane surfaces. Site-speci fic mutagenesis, time-resolved spectroscopy and X-ray diffraction conf irm this mechanism for bacteriorhodopsin, and implicate change of elec trostatic interaction at the active site as the trigger for the global protein conformation change during the proton transport cycle.