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|Section2= |Section7= |Section8= }} Retinal is also known as retinaldehyde. It was originally called retinene, and renamed afterwards it was discovered to be vitamin A aldehyde. Retinal is one of the many forms of vitamin A (the number of which varies from species to species). Retinal is a polyene chromophore, bound to proteins called opsins, and is the chemical basis of animal vision. Retinal allows certain microorganisms to convert light into metabolic energy. Vertebrate animals ingest retinal directly from meat, or they produce retinal from carotenoids, either from one of two carotenes (α-carotene, β-carotene) or from β-cryptoxanthin, a type of xanthophyll. These carotenoids must be obtained from plants or other photosynthetic organisms. No other carotenoids can be converted by animals to retinal, and some carnivores cannot convert any carotenoids at all. The other main forms of vitamin A, retinol, and a partially active form, retinoic acid, may both be produced from retinal. Invertebrates such as insects and squid use hydroxylated forms of retinal in their visual systems, which derive from conversion from other xanthophylls. ==Vitamin A metabolism== Living organisms produce retinal (RAL) by irreversible oxidative cleavage of carotenoids. For example :beta-carotene + O2 → 2 retinal catalyzed by a beta-carotene 15,15'-monooxygenase or a beta-carotene 15,15'-dioxygenase. Just as carotenoids are the precursors of retinal, retinal is the precursor of the other forms of vitamin A. Retinal is interconvertible with retinol (ROL), the transport and storage form of vitamin A :retinal + NADPH + H+ retinol + NADP+ :retinol + NAD+ retinal + NADH + H+ catalyzed by retinol dehydrogenases (RDHs) and alcohol dehydrogenases (ADHs). Retinol is called vitamin A alcohol, or more often, simply vitamin A. Retinal can also be oxidized to retinoic acid (RA) :retinal + NAD+ + H2O → retinoic acid + NADH + H+ (catalyzed by RALDH) :retinal + O2 + H2O → retinoic acid + H2O2 (catalyzed by retinal oxidase) catalyzed by retinal dehydrogenases also known as retinaldehyde dehydrogenases (RALDHs)〔 as well as retinal oxidases.〔(【引用サイトリンク】title=KEGG ENZYME: 1.2.3.11 retinal oxidase )〕 Retinoic acid, sometimes called vitamin A acid, is an important signaling molecule and hormone in vertebrate animals. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「retinal」の詳細全文を読む スポンサード リンク
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