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Retinal
Retinal (also known as retinaldehyde) is a polyene chromophore. Retinal, bound to proteins called opsins, is the chemical basis of visual phototransduction, the light-detection stage of visual perception (vision). Some microorganisms use retinal to convert light into metabolic energy. One study suggests that approximately three billion years ago, most living organisms on Earth used retinal, rather than chlorophyll, to convert sunlight into energy. Because retinal absorbs mostly green light and transmits purple light, this gave rise to the Purple Earth hypothesis. Retinal itself is considered to be a form of vitamin A when eaten by an animal. There are many forms of vitamin A, all of which are converted to retinal, which cannot be made without them. The number of different molecules that can be converted to retinal varies from species to species. Retinal was originally called retinene, and was renamed after it was discovered to be vitamin A aldehyde. Vertebrate animals inge ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vitamin A
Vitamin A is a fat-soluble vitamin that is an essential nutrient. The term "vitamin A" encompasses a group of chemically related organic compounds that includes retinol, retinyl esters, and several provitamin (precursor) carotenoids, most notably Β-Carotene, β-carotene (''beta''-carotene). Vitamin A has multiple functions: growth during embryo development, maintaining the immune system, and healthy vision. For aiding vision specifically, it combines with the protein opsin to form rhodopsin, the light-absorbing molecule necessary for both low-light (scotopic vision) and color vision. Vitamin A occurs as two principal forms in foods: A) retinoids, found in Animal source foods, animal-sourced foods, either as retinol or bound to a fatty acid to become a retinyl ester, and B) the carotenoids Α-Carotene, α-carotene (''alpha''-carotene), β-carotene, Γ-Carotene, γ-carotene (''gamma''-carotene), and the xanthophyll beta-cryptoxanthin (all of which contain β-ionone rings) that ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Opsin
Animal opsins are G-protein-coupled receptors and a group of proteins made light-sensitive via a chromophore, typically retinal. When bound to retinal, opsins become retinylidene proteins, but are usually still called opsins regardless. Most prominently, they are found in photoreceptor cells of the retina. Five classical groups of opsins are involved in Visual perception, vision, mediating the conversion of a photon of light into an electrochemical signal, the first step in the Visual phototransduction, visual transduction cascade. Another opsin found in the mammalian retina, melanopsin, is involved in circadian rhythms and Pupillary light reflex, pupillary reflex but not in vision. Humans have in total nine opsins. Beside vision and light perception, opsins may also sense temperature, sound, or chemicals. Structure and function Animal opsins detect light and are the molecules that allow us to see. Opsins are G-protein-coupled receptors (GPCRs), which are chemoreceptors and hav ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Retinol Dehydrogenase
In enzymology, a retinol dehydrogenase (RDH) () is an enzyme that catalysis, catalyzes the chemical reaction :retinol + NAD+ \rightleftharpoons retinal + NADH + H+ Sometimes, in addition to or along with nicotinamide adenine dinucleotide, NAD+, Nicotinamide adenine dinucleotide phosphate, NADP+ can act as a preferred cofactor in the reaction as well. The substrate of the enzyme can be all-''trans''- or -''cis''- retinol. Some 20 enzymes with RDH activity had been found and studied by 2006. Thus, the two substrate (biochemistry), substrates of this enzyme are retinol and nicotinamide adenine dinucleotide, NAD+, whereas its 3 product (chemistry), products are retinal, nicotinamide adenine dinucleotide, NADH (or NADPH in the case where Nicotinamide adenine dinucleotide phosphate, NADP+ is a cofactor), and hydrogen ion, H+. This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-OH group of donor with NAD+ or NADP+ as acceptor. The List of enzymes, sy ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Visual Phototransduction
Visual phototransduction is the sensory transduction process of the visual system by which light is detected by photoreceptor cells ( rods and cones) in the vertebrate retina. A photon is absorbed by a retinal chromophore (each bound to an opsin), which initiates a signal cascade through several intermediate cells, then through the retinal ganglion cells (RGCs) comprising the optic nerve. Overview Light enters the eye, passes through the optical media, then the inner neural layers of the retina before finally reaching the photoreceptor cells in the outer layer of the retina. The light may be absorbed by a chromophore bound to an opsin, which photoisomerizes the chromophore, initiating both the visual cycle, which "resets" the chromophore, and the phototransduction cascade, which transmits the visual signal to the brain. The cascade begins with graded polarisation (an analog signal) of the excited photoreceptor cell, as its membrane potential increases from a resting po ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Retinol
Retinol, also called vitamin A1, is a fat-soluble vitamin in the vitamin A family that is found in food and used as a dietary supplement. Retinol or other forms of vitamin A are needed for vision, cellular development, maintenance of skin and mucous membranes, immune function and reproductive development. Dietary sources include fish, dairy products, and meat. As a supplement it is used to treat and prevent vitamin A deficiency, especially that which results in xerophthalmia. It is taken by mouth or by intramuscular injection, injection into a muscle. As an ingredient in skin-care products, it is used to reduce wrinkles and other effects of skin aging. Retinol at normal doses is well tolerated. High doses may cause hepatomegaly, enlargement of the liver, dry skin, and hypervitaminosis A. High doses during pregnancy may harm the fetus. The body converts retinol to retinal and retinoic acid, through which it acts. Retinol was discovered in 1909, isolated in 1931, and first m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dehydroretinal
Dehydroretinal (3,4-dehydroretinal) is a derivative metabolite of retinal belonging to the group of vitamin A2 as a retinaldehyde form, besides the endogenously present 3,4-dehydroretinol and 3,4-dehydroretinoic acid. The livers of some freshwater fishes and some fish found in India contain a higher ratio of dehydroretinal to retinal than do other species. See also * Retinene The retinenes (retinene1 and retinene2) are derivative (chemistry), chemical derivatives of vitamin A (see retinol) formed through oxidation reactions. Retinene1 is better known as retinal and is fundamental in the transduction of light into visua ... References Vision Signal transduction Apocarotenoids Photosynthetic pigments Vitamins {{organic-compound-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Purple Earth Hypothesis
The Purple Earth Hypothesis (PEH) is an astrobiological hypothesis, first proposed by molecular biologist Shiladitya DasSarma in 2007, that the earliest photosynthetic life forms of Early Earth were based on the simpler molecule retinal rather than the more complex porphyrin-based chlorophyll, making the surface biosphere appear purplish rather than its current greenish color. It is estimated to have occurred between 3.5 and 2.4 billion years ago during the Archean eon, prior to the Great Oxygenation Event and Huronian glaciation. Retinal-containing cell membranes exhibit a single light absorption peak centered in the energy-rich green-yellow region of the visible spectrum, but transmit and reflect red and blue light, resulting in a magenta color. Chlorophyll pigments, in contrast, absorb red and blue light, but little or no green light, which results in the characteristic green reflection of plants, green algae, cyanobacteria and other organisms with chlorophyllic organelles. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Retinene
The retinenes (retinene1 and retinene2) are derivative (chemistry), chemical derivatives of vitamin A (see retinol) formed through oxidation reactions. Retinene1 is better known as retinal and is fundamental in the transduction of light into visual signals in the photoreceptor cell, photoreceptor level of the retina (known as the visual cycle). Retinene2 is more formally known as dehydroretinal. The energy of impinging photons will convert retinal, retinaldehyde from an 11-cis isomer into an all-trans form. In the retina, this conversion induces a conformational change in the surrounding opsin 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 densit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Beta-carotene 15,15'-monooxygenase
In enzymology, beta-carotene 15,15'-dioxygenase, () is an enzyme with systematic name ''beta-carotene:oxygen 15,15'-dioxygenase (bond-cleaving)''. In human it is encoded by the ''BCO1'' gene. This enzyme catalyses the following chemical reaction : beta-carotene + O2 → 2 all-''trans''-retinal This is a cleavage reaction which cleaves β-carotene, utilizes molecular oxygen, is enhanced by the presence of bile salts and thyroxine, and generates two molecules of retinal. In humans, the enzyme is present in the small intestine and liver. The dioxygenase also asymmetrically cleaves beta-cryptoxanthin, ''trans''-β-apo-8'-carotenal, beta-4'-apo-β-carotenal, alpha-carotene and gamma-carotene in decreasing order, creating one retinal molecule, all of these being substrates with a carbon chain greater than C30, with at least one unsubstituted β-ionone ring. This enzyme belongs to the (enzymatically-defined) family of oxidoreductase In biochemistry, an oxidoreductase is an en ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Retinoic Acid
Retinoic acid (simplified nomenclature for all-''trans''-retinoic acid) is a metabolite of vitamin A1 (all-''trans''-retinol) that is required for embryonic development, male fertility, regulation of bone growth and immune function. All-''trans''-retinoic acid is required for chordate animal development, which includes all higher animals from fish to humans. During early embryonic development, all-''trans''-retinoic acid generated in a specific region of the embryo helps determine position along the embryonic anterior/posterior axis by serving as an intercellular signaling molecule that guides development of the posterior portion of the embryo. It acts through Hox genes, which ultimately control anterior/posterior patterning in early developmental stages. In adult tissues, the activity of endogenous retinoic acid appears limited to immune function and male fertility. All-''trans''-retinoic acid is the major occurring retinoic acid, while isomers like 13-''cis''- and 9-''cis''-r ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Xanthophylls
Xanthophylls (originally phylloxanthins) are yellow pigments that occur widely in nature and form one of two major divisions of the carotenoid group; the other division is formed by the carotenes. The name is from Greek: (), meaning "yellow", and (), meaning "leaf"), due to their formation of the yellow band seen in early chromatography of leaf pigments. Molecular structure As both are carotenoids, xanthophylls and carotenes are similar in structure, but xanthophylls contain oxygen atoms while carotenes are ''purely hydrocarbons'', which do not contain oxygen. Their content of oxygen causes xanthophylls to be more polar (in molecular structure) than carotenes, and causes their separation from carotenes in many types of chromatography. (Carotenes are usually more orange in color than xanthophylls.) Xanthophylls present their oxygen either as hydroxyl groups and/or as hydrogen atoms substituted by oxygen atoms when acting as a bridge to form epoxides. Occurrence Like other c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
