Retinene
Encyclopedia
The Retinenes are chemical derivatives of the dietary supplement vitamin
A (see retinol
) formed through oxidation reactions.
Retinene1 is better known as retinaldehyde or simply retinal
and is fundamental in the transduction of light into visual signals in the photoreceptor level of the retina
(known as the visual cycle). Retinene2 is more formally known as dehydroretinaldehyde.
The energy of impinging photon
s will convert retinaldehyde
from an 11-cis isomer
into an all-trans form. In the retina, this conversion induces a conformational change in the surrounding photopsin
protein
pigment, leading to signaling through the G protein
transducin
. Retinaldehyde also forms a part of bacteriorhodopsin
, a light-induced proton pump
found in some archaea
.
Experimentally, it is possible to replace 11-cis retinaldehyde by perfusing retinal tissue preparations with retinaldehyde derivatives. Selective modification of the retinaldehyde structure, particularly the density of electrons in the π-orbitals, can lead to insights into the interaction between the retinaldehyde moiety and the surrounding pigment protein.
"The names of all these molecules have recently been changed ... vitamin A is now retinol
, retinene is retinal
; there is also retinoic acid
"—George Wald
(1967).
Vitamin
A vitamin is an organic compound required as a nutrient in tiny amounts by an organism. In other words, an organic chemical compound is called a vitamin when it cannot be synthesized in sufficient quantities by an organism, and must be obtained from the diet. Thus, the term is conditional both on...
A (see retinol
Retinol
Retinol is one of the animal forms of vitamin A. It is a diterpenoid and an alcohol. It is convertible to other forms of vitamin A, and the retinyl ester derivative of the alcohol serves as the storage form of the vitamin in animals....
) formed through oxidation reactions.
Retinene1 is better known as retinaldehyde or simply retinal
Retinal
Retinal, also called retinaldehyde or vitamin A aldehyde, is one of the many forms of vitamin A . Retinal is a polyene chromophore, and bound to proteins called opsins, is the chemical basis of animal vision...
and is fundamental in the transduction of light into visual signals in the photoreceptor level of the retina
Retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
(known as the visual cycle). Retinene2 is more formally known as dehydroretinaldehyde.
The energy of impinging photon
Photon
In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...
s will convert retinaldehyde
Retinal
Retinal, also called retinaldehyde or vitamin A aldehyde, is one of the many forms of vitamin A . Retinal is a polyene chromophore, and bound to proteins called opsins, is the chemical basis of animal vision...
from an 11-cis isomer
Isomer
In chemistry, isomers are compounds with the same molecular formula but different structural formulas. Isomers do not necessarily share similar properties, unless they also have the same functional groups. There are many different classes of isomers, like stereoisomers, enantiomers, geometrical...
into an all-trans form. In the retina, this conversion induces a conformational change in the surrounding photopsin
Photopsin
Photopsins 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...
protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
pigment, leading to signaling through the G protein
G protein
G proteins are a family of proteins involved in transmitting chemical signals outside the cell, and causing changes inside the cell. They communicate signals from many hormones, neurotransmitters, and other signaling factors. G protein-coupled receptors are transmembrane receptors...
transducin
Transducin
Transducin is a heterotrimeric G protein that is naturally expressed in vertebrate retina rods and cones .- Mechanism of action :...
. Retinaldehyde also forms a part of bacteriorhodopsin
Bacteriorhodopsin
Bacteriorhodopsin is a protein used by Archaea, the most notable one being Halobacteria. It acts as a proton pump; that is, it captures light energy and uses it to move protons across the membrane out of the cell...
, a light-induced proton pump
Proton pump
A proton pump is an integral membrane protein that is capable of moving protons across a cell membrane, mitochondrion, or other organelle. Mechanisms are based on conformational changes of the protein structure or on the Q cycle.-Function:...
found in some archaea
Archaea
The Archaea are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon...
.
Experimentally, it is possible to replace 11-cis retinaldehyde by perfusing retinal tissue preparations with retinaldehyde derivatives. Selective modification of the retinaldehyde structure, particularly the density of electrons in the π-orbitals, can lead to insights into the interaction between the retinaldehyde moiety and the surrounding pigment protein.
"The names of all these molecules have recently been changed ... vitamin A is now retinol
Retinol
Retinol is one of the animal forms of vitamin A. It is a diterpenoid and an alcohol. It is convertible to other forms of vitamin A, and the retinyl ester derivative of the alcohol serves as the storage form of the vitamin in animals....
, retinene is retinal
Retinal
Retinal, also called retinaldehyde or vitamin A aldehyde, is one of the many forms of vitamin A . Retinal is a polyene chromophore, and bound to proteins called opsins, is the chemical basis of animal vision...
; there is also retinoic acid
Retinoic acid
Retinoic acid is a metabolite of vitamin A that mediates the functions of vitamin A required for growth and development. Retinoic acid is required in chordate animals which includes all higher animals from fishes to humans...
"—George Wald
George Wald
George Wald was an American scientist who is best known for his work with pigments in the retina. He won a share of the 1967 Nobel Prize in Physiology or Medicine with Haldan Keffer Hartline and Ragnar Granit.- Research :...
(1967).