Proton Pump Caught in the Act

How does a protein pump protons in only one direction? In his Perspective, Gennis explains how this occurs in bacteriorhodopsin, a membrane protein that pumps protons in response to light stimulation. A new structure by Luecke et al. on p. 255 shows that small changes in the conformation within bacteriorhodopson induced as a result of light absorption by retinal, are sufficient to change the pK9s of several key residues enough to promote the release of protons on one side of the membrane.

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