Photopsin
Photopsins are the photoreceptor proteins found in the cone cells of the retina that are the basis of color vision. Iodopsin, the cone pigment system in chicken retina, is a close analog of the visual purple rhodopsin that is used in night vision. Iodopsin consists of the protein component and a bound chromophore, 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 epigenetic changes.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 |
| S - "tritan", "cyanolabe" | β | 400-500 nm | 420–440 nm |
| M - "deutan", "chlorolabe" | γ | 450-630 nm | 534–545 nm |
| L - "protan", "erythrolabe" | ρ | 500-700 nm | 564–580 nm |
Humans have three different photoreceptor proteins which are found in cone cells and which are responsible for colour vision:
- Long Wavelength Sensitive Opsin - λmax of 560 nm, in the yellow-green region of the electromagnetic spectrum. May be called the "red opsin," "erythrolabe," "L opsin" or "LWS opsin." Note that despite its common name as the "red" opsin, this opsin's peak sensitivity is not in the red region of the spectrum. However, it is more sensitive to red than the other two human opsins. This receptor also has a secondary response in the violet high frequencies
- Middle Wavelength Sensitive Opsin - λmax of 530 nm, in the green region of the electromagnetic spectrum. May be called the "green opsin," "chlorolabe," "M opsin" or "MWS opsin."
- Short Wavelength Sensitive Opsin - λmax of 430 nm, in the blue region of the electromagnetic spectrum. May be called the "blue opsin," "cyanolabe," "S opsin" or "SWS opsin."
History