Visual Pigment


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visual pigment

[′vizh·ə·wəl ′pig·mənt]
(biochemistry)
Any of various photosensitive pigments of vertebrate and invertebrate photoreceptors.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

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

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
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.
This visual pigment, with [[lambda].sub.max] = 464 nm, is well suited for operating in the shallow marine habitats of S.
Although we identify several transcriptomic sequences that putatively encode key components for a typical [G.sub.q]-mediated phototransduction pathway, more data are required to confirm that the recovered opsin transcripts produce functional visual pigments of different spectral sensitivities or that they use a [G.sub.q]-mediated phototransduction pathway.
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 spectral absorbance curves of the two different visual pigments peaked with one [alpha]-band at 510 nm and a [beta]-band at around 380 nm; and the other [alpha]-band at 380 nm as predicted by the template of Stavenga et al.
The best-fit visual pigment absorptance curve has a [[lambda].sub.max] of 487 nm and visual pigment specific absorbance of 0.013 [micro][m.sup.-1] (residual sum of squares = 0.123) (Fig.
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., (1998).
Since the discovery of an ultraviolet (UV) visual pigment in the retina of the Japanese dace (1), other freshwater fishes have been found to possess UV pigments (2).
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.