Visual Pigment


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visual pigment

[′vizh·ə·wəl ′pig·mənt]
(biochemistry)
Any of various photosensitive pigments of vertebrate and invertebrate photoreceptors.

Visual Pigment

 

a structural and functional unit of the photosensitive membrane of the photoreceptors of the retina, the rods and cones. The first stage of visual perception—the absorption of quanta of visible light—takes place in the visual pigment. A molecule of visual pigment (molecular mass, approximately 40,000) consists of a chromophore that absorbs light and opsin, a complex of protein and phospholipids. The chromophore of all visual pigments is an aldehyde of vitamin A, or A,—retinal or 3-dehydroretinal. The two forms of opsin (rod and cone) and the two forms of retinal unite in pairs and form four types of visual pigment that differ from one another in their absorption spectra: rhodopsin, or visual purple (the most common rod visual pigment; maximum absorption 500 nanometers [nm]), iodopsin (562 nm), porphyropsin (522 nm), and cyanopsin (620 nm). The primary photochemical link in the mechanism of vision consists in the photoisomerization of retinal, which, under the action of light, changes its curved configuration to a flat one. A chain of dark processes follows this reaction; they lead to the emergence of a visual receptor signal, which is then synaptically transmitted to the sequent nerve elements of the retina—the bipolar and horizontal cells.

REFERENCES

Fiziologiia sensornykh sistem, part 1. Leningrad, 1971. Pages 88-125. (Rukovodstvo po fiziologii.)
Wald, G. “The Molecular Basis of Visual Excitation. ”Nature, 1968, vol. 219.

M. A. OSTROVSKII

References in periodicals archive ?
Coexpression of two visual pigments in a photoreceptor causes an abnormally broad spectral sensitivity in the eye of the butterfly Papilio xuthus.
4B, thin black line), which blocks most light below 550 nm and efficiently acts as a screening pigment for the blue-green-absorbing visual pigment in the marine habitat.
Our data do not necessarily support one evolutionary progression over the other, but the question of which came first--opsins used for visual tasks or those used for nonvisual tasks--is one that certainly warrants further study in stomatopods, which are well known for their eyes that include a diversity of visual pigments.
The RPE cells perform several functions, including absorption of light, enabling the turnover of photoreceptor outer segments, formation of visual pigments by storing and releasing vitamin A.
exoculata has a visual pigment, and it has it in very large quantities -- at the very least five times more than the usual amount of pigment in other shrimp," he says.
The best-fit visual pigment absorptance curve has a [[lambda].
Now that the visual pigment genes have been identified, scientists expect to be able to obtain for the first time adequate amounts of the pigments for biochemical study.
This suggests that they may be visible to predators whose color discrimination at blue and green wavelengths is good owing to multiple visual pigments or ocular filters.
The structure of arthropod photoreceptors naturally makes them sensitive to the plane of polarization of incoming light, because the visual pigments that absorb light are dichroic and are oriented mostly parallel in small, tubular membranes called microvilli.
Visual pigment absorption was measured with a single beam, wavelength scanning, computer-controlled microspectrophotometer described by Hart et al.
This measurement suggests that the primary visual pigment chromophore in this retina is vitamin [A.
As cuttlefish are likely to have a single visual pigment (8) with maximal absorption near 490 nm [ILLUSTRATION FOR FIGURE 1A OMITTED], such short-wavelength blocking compounds would be expected to have a small impact on the cuttlefish visual sensitivity.