QUANTITATIVE-EVALUATION OF THE DYNAMICS OF PROTON-TRANSFER FROM PHOTOACTIVATED BACTERIORHODOPSIN TO THE BULK

It has been reported by many research groups that protons released dur ing the photocycle of bacteriorhodopsin are detected by surface bound indicators much faster than by indicators in the bulk, In this study w e used numerical simulation of chemical reaction's dynamics for analyz ing the delayed appearance of protons in the bulk. The results indicat e that the low pK surface groups of the membrane, which form an undilu table concentrated matrix of proton binding sites, retain the protons in this space according to the mass action law. The main sites for pro ton accumulation are the cluster of carboxylates on the cytoplasmic si de of the membrane, The protonation of an indicator in the bulk does n ot proceed by its reaction with free proton, but rather through self-d iffusion of the indicator to the membrane and abstraction of proton fr om the protonated surface group. The detailed mechanisms which corresp ond with these reactions are reported.