Photons induce isomerization of 11c-retinyl to at-retinyl

Stable Identifier
Reaction [transition]
Homo sapiens
Rhodopsin activation
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The visual pigment rhodopsin consists of a seven transmembrane helix protein, opsin (RHO), to which an 11-cis-retinal (11cRAL) chromophore is bound as a protonated Schiff base (Hargrave et al. 1983, Nathans & Hogness 1984, Ovchinnikov et al. 1983). The covalent bond between opsin and its 11-cis-retinyl (11c-retinyl) ligand, which is unique among G protein coupled receptors, helps to confer extraordinary stability in darkness (Baylor et al. 1984). 11cRAL is an inverse agonist, that quenches the weak ability of opsin to activate transducin G protein (Gt). Upon photon absorption, the bound 11c-retinyl group isomerizes in a few hundred femtoseconds (Schoenlein et al. 1991) and with a high quantum efficiency of 0.7 (Dartnall 1968) to the bound all-trans-retinyl (at-retinyl) isomer. Then in the next few milliseconds, opsin undergoes a rearrangement in structure that renders it catalytically active (MII aka metarhodopsin II or R*) (Emeis et al. 1982). The isomerisation is a very fast photochemical process (femtoseconds) followed by slower events (Smith 2010).

Mutations in RHO can give rise to autosomal dominant or recessive forms of retinitis pigmentosa or autosomal dominant congenital stationary night blindness ( Retinitis pigmentosa is a progressive form of blindness marked by an initial degeneration of rods, followed by the secondary loss of cones.

Literature References
PubMed ID Title Journal Year
20192770 Structure and activation of the visual pigment rhodopsin

Smith, SO

Annu Rev Biophys 2010
6679757 [Visual rhodopsin. III. Complete amino acid sequence and topography in a membrane]

Ovchinnikov, IuA, Abdulaev, NG, Feĭgina, MIu, Artamonov, ID, Bogachuk, AS

Bioorg. Khim. 1983
6342691 The structure of bovine rhodopsin

Hargrave, PA, McDowell, JH, Curtis, DR, Wang, JK, Juszczak, E, Fong, SL, Rao, JK, Argos, P

Biophys. Struct. Mech. 1983
6288450 Complex formation between metarhodopsin II and GTP-binding protein in bovine photoreceptor membranes leads to a shift of the photoproduct equilibrium

Emeis, D, Kühn, H, Reichert, J, Hofmann, KP

FEBS Lett. 1982
6512705 The photocurrent, noise and spectral sensitivity of rods of the monkey Macaca fascicularis

Baylor, DA, Nunn, BJ, Schnapf, JL

J. Physiol. (Lond.) 1984
6589631 Isolation and nucleotide sequence of the gene encoding human rhodopsin.

Nathans, J, Hogness, DS

Proc Natl Acad Sci U S A 1984
1925597 The first step in vision: femtosecond isomerization of rhodopsin

Schoenlein, RW, Peteanu, LA, Mathies, RA, Shank, CV

Science 1991
5315589 The photosensitivities of visual pigments in the presence of hydroxylamine

Dartnall, HJ

Vision Res. 1968
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