title: On the mechanism of hydrogen-deuterium exchange in bacteriorhodopsin.
abstract: Continuous-flow resonance Raman experiments carried out in bacteriorhodopsin show that the exchange of a deuteron on the Schiff base with a proton takes place in times shorter than 3 ms. Exchange mechanisms based on a base-catalyzed deprotonation followed by reprotonation of the Schiff base are excluded. A mechanism is suggested in which a water molecule interacts directly with the Schiff base deuteron in a concerted exchange mechanism. It appears that in the dark, the binding site is more accessible to neutral water molecules than to charged protons.
mesh_terms: D001436:Bacteriorhodopsins; D002338:Carotenoids; D055598:Chemical Phenomena; D002621:Chemistry; D003903:Deuterium; D006859:Hydrogen; D006863:Hydrogen-Ion Concentration; D012545:Schiff Bases; D013059:Spectrum Analysis, Raman
chemical_list: D012545:Schiff Bases; D002338:Carotenoids; D001436:Bacteriorhodopsins; D006859:Hydrogen; D003903:Deuterium