| 单词 | vitamin a₁ |
| 释义 | > as lemmasvitamin A₁ vitamin A n. either or both of two closely related fat-soluble vitamins, A₁ and A₂, esp. the former; = retinol n.2; vitamin A₁, an alcohol that is present (as fatty acid esters) in egg-yolk, liver, butter, and milk, is also formed in the body from carotenoids present in green vegetables and stored in the liver, and is a component of the visual pigment rhodopsin; a deficiency of vitamin A₁ leads to night blindness and anæmia and ultimately xerophthalmia and blindness, vitamin A₂, the analogous component of the visual pigment porphyropsin in freshwater fish. ΚΠ 1920Vitamin A [see sense 1]. 1937 J. R. Edisbury in Nature 7 Aug. 234/1 A substance apparently identical with the 693 mμ chromogen can replace the vitamin A of rhodopsin without loss of physiological function... It..seems desirable provisionally to designate as ‘vitamin A2’ the 693 mμ chromogen. 1950 Sci. News 15 17 Kühne found, when visual purple is acted on by light, that a new substance is formed which he called visual yellow. The latter has now been shown to be closely related to, if not identical with, the aldehyde of vitamin A1, called retinene-1. 1960 Jrnl. Amer. Chem. Soc. 82 5581/1 The pure substance hitherto known as vitamin A1 or axerophthol shall be designated retinol. 1968 A. White et al. Princ. Biochem. (ed. 4) xl. 906 Vitamin A2 differs from A1 by having one additional conjugated double bond in the ring. 1976 H. R. Schiffman Sensation & Perception xii. 184/2 When the eye is kept in the dark, vitamin A joins with opsin to reconstitute rhodopsin. 1982 S. G. Chaney in T. M. Devlin Textbk. Biochem. xxvi. 1202 Vitamin A is also apparently required for mobilization of iron from the liver. < as lemmas |
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