Photopsin

Photopsin
Normalised absorption spectra of the three human photopsins and of human rhodopsin (dashed).

Photopsins (also known as iodopsins) are the photoreceptor proteins found in the cone cells of the retina that are the basis of color vision. Photopsins are very close analogs of the visual purple rhodopsin that is used in night vision. Photopsins consist of a protein called opsin and a bound chromophore, the retinal.

Contents

Function

Opsins are Gn-x protein-coupled receptors of the retinylidene protein family. Isomerization of 11-cis-retinal into all-trans-retinal by light induces a conformational change in the protein that activates photopsin and promotes its binding to G protein transducin, which triggers a second messenger cascade.

Types

Different opsins differ in a few amino acids and absorb light at different wavelengths as retinal-bound pigments.

Cone type Name Range Peak wavelength[1][2]
S (OPN1SW) - "tritan", "cyanolabe" β 400–500 nm 420–440 nm
M (OPN1MW) - "deutan", "chlorolabe" γ 450–630 nm 534–545 nm
L (OPN1LW) - "protan", "erythrolabe" ρ 500–700 nm 564–580 nm

In humans there are three different iodopsins (rhodopsin analogs) that form the protein-pigment complexes photopsin I, II, and III. They are called erythrolabe, chlorolabe, and cyanolabe, respectively.[3] These photopsins have absorption maxima for yellowish-green (photopsin I), green (photopsin II), and bluish-violet light (photopsin III).

History

George Wald got the 1967 Nobel Prize in Physiology or Medicine for his experiments in the 1950s that showed the difference in absorbance by these photopsins (see image).

See also

  • Rhodopsins, the pigment for monochromatic (scotopic) dark vision.
  • Melanopsin, the pigment which is used to control pupil sizes and the sleep/wake cycle
  • Visual cycle, the chemistry of phototransduction
  • Color blindness

References

  1. ^ Wyszecki, Günther; Stiles, W.S. (1982). Color Science: Concepts and Methods, Quantitative Data and Formulae (2nd ed.). New York: Wiley Series in Pure and Applied Optics. ISBN 0-471-02106-7. 
  2. ^ R. W. G. Hunt (2004). The Reproduction of Colour (6th ed.). Chichester UK: Wiley–IS&T Series in Imaging Science and Technology. pp. 11–12. ISBN 0-470-02425-9. 
  3. ^ Rushton, W. A. H. (1 June 1966). "Densitometry of pigments in rods and cones of normal and color defective subjects" (PDF). Investigative Ophthalmology 5 (3): 233–241. PMID 5296487. http://www.iovs.org/cgi/content/abstract/5/3/233. Retrieved 2006-11-14. 

External links



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Look at other dictionaries:

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  • photopsin — The protein moiety (opsin) of the pigment (iodopsin) in the cones of the retina. * * * pho·top·sin (fo topґsin) the opsin of the cones of the retina that combines with 11 cis retinal to form photochemical pigments (iodopsins). See illustration at …   Medical dictionary

  • Opsin — bezeichnet den Proteinanteil eines Sehpigments, das insgesamt aus dem Protein sowie einem Chromophor besteht. Im englischen Sprachraum wird oft das gesamte Sehpigment als Opsin bezeichnet. Opsine gehören zur Superfamilie der heptahelicalen… …   Deutsch Wikipedia

  • Iodopsin — (Jodopsin) ist die Sammelbezeichnung für die Farbsehpigmente der Zapfen von Tieren. Es handelt sich um Photopsine (das sind Proteine) in kovalenter Bindung mit jeweils einem farbgebenden Stoff (Chromophor) des Typs 1: Neoretinin (11 cis Retinol)… …   Deutsch Wikipedia

  • Rhodopsin — Rhodopsin, also known as visual purple, is a pigment of the retina that is responsible for both the formation of the photoreceptor cells and the first events in the perception of light. Rhodopsins belong to the G protein coupled receptor family… …   Wikipedia

  • Retinylidene protein — Retinylidene proteins are a family of proteins that use retinal as chromophore for light reception. This group of proteins is also commonly referred to as rhodopsins. They are the molecular basis for a variety of light sensing systems from… …   Wikipedia

  • Cyanopsin — (von griechisch kyanos ‚blau‘) ist eine veraltete Bezeichnung für zwei verschiedene Sehpigmente: als Cyanopsin wurde früher das in den Zapfen der Süßwasserfische und vieler Amphibien vorkommende, cyanfarbene Porphyropsin bezeichnet.[1] Das… …   Deutsch Wikipedia

  • Crystallin — Not to be confused with Crystalline. In anatomy, a crystallin is a water soluble structural protein found in the lens and the cornea of the eye accounting for the transparency of the structure.[1] It has also been identified in other places such… …   Wikipedia

  • Retinene — The Retinenes (Retinene1 and Retinene2) are chemical derivatives of the dietary supplement vitamin A (see retinol) formed through oxidation reactions.Retinene1 is better known as retinaldehyde or simply retinal and is fundamental in the… …   Wikipedia

  • Melanopsin — Opsin 4 Identifiers Symbols OPN4; MGC142118; MOP External IDs OMIM:  …   Wikipedia

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