Figure 11

Figure 11. Schematic of the proposed proton transfer mechanism for switching the protonated Schiff-base (PSB) counterion in rhodopsin. (a) Rhodopsin: two water molecules and Ser-186 form a H-bond chain between Glu-113 and Glu-181. Electrostatic interaction between the PSB and Glu-113 is indicated by the green dashed line. (b) Blue-shifted intermediate: after photoisomerization, the H-bond chain evolves so that the two water molecules and Ser-186 are lined up to prepare for the proton transfer and the PSB has shifted relative to Glu-113. (c) Lumirhodopsin: the PSB shifts further away from Glu-113 toward Glu-181. The gray arrows indicate a possible proton transfer pathway. (d) Metarhodopsin I: proton transfer is completed. The PSB group is now close to Glu-181 to establish the electrostatic interaction (green dashed line) with the new counterion. Reprinted from Yan et al., 2003 (67).

From: Phototransduction in Rods and Cones

Cover of Webvision
Webvision: The Organization of the Retina and Visual System [Internet].
Kolb H, Fernandez E, Nelson R, editors.
Salt Lake City (UT): University of Utah Health Sciences Center; 1995-.

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