RHODOPSIN

From Big Medical Encyclopedia

RHODOPSIN (synonym rhodopsin) — one of rhodopsins of photoreceptors of a retina of an eye. The pathology connected with R. and a photoreceptor membrane can be the cause of a serious eye illness — various forms of a retinal abiotrophy of an eye (see. Tapetoretinalny dystrophies ).

The river represents the chromoglycoprotein which is strongly connected with a membrane of a photoreceptor cell (see. Fotoretseptora ). The molecule P. consists of a proteinaceous part — opsin, chromophoric and carbohydrate parts; its pier. the weight (weight) apprx. 38 000. The polypeptide chain of opsin includes apprx. 350 remains of amino acids, primary structure of opsin is not established. Chromophoric group in a molecule P. is the retinal (which was earlier called retinene) — aldehyde of vitamin A (see. Retinolum ), to-ry it is covalently connected with 8 amino group of the rest of a lysine of a proteinaceous part of a molecule. The retinal is in a molecule P. in 11 - cis-to a form (see. Isomerism ). Rhodopsins of vertebrate and backboneless animals contain the same chromophore — 11 - cis-a retinal, but protein (opsin) at them is species-specific. A carbohydrate part of a molecule P. represents two oligosakharidny chains connected by a covalent bond with NH 2 - end of a polypeptide chain of River. A polypeptide chain of a molecule P., being several times bent, «stitches» through a photoreceptor membrane. R. in a membrane asymmetrically is located; in a disk of an outside segment of a stick of vertebrate animals and probably the person the COOH trailer site of a polypeptide chain is located on a hydrophilic surface of a cytoplasmic membrane, NH 2 - the tail of a molecule P. is on an opposite surface, in intra disk space; the most part of the most polypeptide chain of R. is shipped in a hydrophobic part of a lipidic dimolecular layer of a membrane (see. Membranes biological ). Such transmembrane arrangement of a molecule P., most likely, is essentially important for implementation of one of its functions connected with increase in permeability of a membrane for ions during the lighting. The membrane of photoreceptors has exclusively light body, and the molecule P. shipped in it is exposed to Brownian motion, undergoing bystry rotary and slower lateral diffusion, in the course the cut can be provided interaction of a molecule P. in the dark or decoloured state with other molecules of proteins in a photoreceptor membrane.

The maximum of absorption of R. is in a visible part of a range at wavelength apprx. 500 nanometers and defines a maximum of spectral response of sticks retinas (see) eyes (see) and respectively maximum of curve visibility night or twilight, i.e. scotopic, sight (see). The pure retinal has yellow color, its maximum of absorption is at 370 nanometers.

Carry to R. also a rhodopsin of krasnochuvstvitelny flasks of a retina of the person and other vertebrata — iodopsin, chromophoric group to-rogo also is 11 - cis-a retinal.

The rhodopsins containing in quality of chromophoric group 11 - cis-3-degidroretinal, are called porfiropsina (see. Rhodopsins ). In bacteria one more retinalsoderzhashchy protein, a bacterial analog of rhodopsin is found, so-called bakteriorodopsinony It is the chromoproteid consisting of hydrophobic protein and a retinal in 13 - cis-or a transform. The bacteriorhodopsin, as well as R., is transmembrane protein. Main function of a bacteriorhodopsin biopower. Energy of light absorbed by a retinal is used by a bacteriorhodopsin for active transfer of a proton through a so-called purple membrane of salt-loving bacteria therefore on it electrochemical potential is created, energy to-rogo, in turn, is used for synthesis of ATP. It is the elementary, ancient achlorophyllous form photosynthesis (see).

Actually photochemical reaction in sight (see. Photochemical reactions ) reaction of a photoisomerization of a retinal of R. is: at absorption of a light quantum a molecule P. the last completely passes from 11 - cis-in a transform. This reaction initiates a series of conformational changes of R. that eventually leads to change of permeability of a membrane of a photoreceptor for ions and generation on it the receptor potential (a photoreceptor signal). The difficult mechanism of interface between photochemical reaction in R. and generation of receptor potential remains not found out yet.

In the course of regeneration of molecules P. at vertebrata the large role is played by an enzymatic isomerization of a trans-retinal again in cis-form. However there are no direct characteristics of this process and the enzymes participating in it yet.

See also Pigments .



Bibliography: Ostrovsky M. A. Problem of a rhodopsin of rhodopsin and bacteriorhodopsin, Vestn. Academy of Sciences of the USSR, No. 9, page 120, 1979; it, Visual reception — a problem on a joint of sciences, Science in the USSR, No. 1, page 71, 1981; Ostrovsky M. A. and Fedorovich I. B. The photoinduced changes of a photoreceptor membrane, in book: Structure and functions biol. membranes, under the editorship of A.S. Troshin, etc., page 224, M., 1975, bibliogr.; they, Photochemical transformations of a rhodopsin — rhodopsin, Quantum electronics, t. 5, No. 10, page 2263,1978; Hub bell W. L. and. In o w n d s M. D. Visual transduction in vertebrate photoreceptors, Ann. Rev. Neurosci., v. 2, p. 17,1979; Montal M. Rhodopsin in model membranes, Biochim. biophys. Acta (Amst.), v. 559, p. 231, 1979; Ostroy S. E. Rhodopsin and the visual process, ibid., v. 463, p. 91, 1977.


M. A. Ostrovsky.

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