Photopsin
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Overview
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.
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][1] |
|---|---|---|---|
| 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.[1] 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
External links
- Rhodopsin and the eye, an excellent summary with pictures.de:Iodopsin
Eye proteins | |
|---|---|
| Opsin (retinylidene protein) | Rhodopsin - Melanopsin - Photopsin |
| Crystallin | Alpha crystallin |
| Other | Arrestin - Guanylate cyclase activator - Recoverin - Rhodopsin kinase |
Acknowledgement and Attribution Regarding Sources of Content
Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .
