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Issue 11, 2010
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Multiple functions of Schiff base counterion in rhodopsins

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In rhodopsins, visible-light absorption is achieved by the protonation of the chromophore Schiff base. The Schiff base proton is stabilized by the negative charge of an amino acid residue called the Schiff base counterion. Since E113 was identified as the counterion in bovine rhodopsin, there has been growing evidence that the counterion has multiple functions besides proton stabilization. Here, we first introduce generally accepted findings as well as some controversial theories about the identity of the Schiff base counterion in the dark and in intermediate states and then review multiple functions of the counterion in vertebrate visual pigments. Special focus is placed on the recently demonstrated role in photoisomerization efficiency. Finally, differences in the position of the counterion between vertebrate visual pigments and other opsins and its relevance to the molecular evolution of opsins are discussed.

Graphical abstract: Multiple functions of Schiff base counterion in rhodopsins

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The article was received on 03 Jun 2010, accepted on 06 Aug 2010 and first published on 14 Sep 2010

Article type: Perspective
DOI: 10.1039/C0PP00134A
Photochem. Photobiol. Sci., 2010,9, 1426-1434

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    Multiple functions of Schiff base counterion in rhodopsins

    K. Tsutsui and Y. Shichida, Photochem. Photobiol. Sci., 2010, 9, 1426
    DOI: 10.1039/C0PP00134A

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