Biochemical mechanisms of vitamin A action
Biochemical mechanisms of vitamin A action
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维生素A作用的生化机制
DOI：
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发表时间：
1983
影响因子：
7
通讯作者：
F. Weber
中科院分区：
文献类型：
--
作者：
F. Weber
众所周知，维生素A在各种动物和人体组织中具有多种生理功能。它对于刺激骨骼组织的生长和正常发育、正常生殖、维持视棒视觉以及最重要的是保存粘液分泌上皮组织的分化功能至关重要（比较De Luca, 1977; Ganguly el al. 1980; Navia & Harris, 1980）。因此，饮食中缺乏维生素A会导致临床缺乏症状，如生长迟缓、骨骼畸形、生殖器官退化、夜盲症和严重的上皮结构改变，包括结膜和角膜干眼症，可能导致角膜软化，最终失明。然而，上皮化生不仅发生在眼睛，也发生在呼吸道、胃肠道和泌尿生殖道的上皮。组织病理学上，上皮的粘液分泌层被层状、鳞状和角化上皮所取代，但肠黏膜不角化。由于这些广泛的生理功能，维生素A是维持健康和生命的最重要的营养素之一。因此，许多生物化学家投入了大量的研究工作来阐明维生素a在细胞和分子水平上的作用方式。虽然维生素A直接参与视觉兴奋的过程已经确定，但维生素A的一般分子功能仍在研究中，目前这些研究主要集中在维生素A在细胞分化中的基本作用上。在视觉过程中，维生素A起着非常特殊的作用。这主要体现在乔治·沃尔德（George Wald）及其同事的杰出研究工作上（Wald, 1968）。维生素A以醛（视网膜）的形式与感光色素视紫红质和碘紫红质结合，这两种色素分别位于脊椎动物的杆状细胞和视锥细胞的外节。视锥细胞是高强度光的感受器，就人类视锥细胞而言，是彩色视觉的感受器，而视杆细胞对低强度光特别敏感。维生素A缺乏会导致视紫红质的合成减少，从而产生黑暗适应问题。几个反应，包括氧化或还原和维生素A分子的构型变化发生在视觉周期。维生素A以长链脂肪酸酯的形式储存在视网膜色素上皮中，在人类中，除了肝脏外，视网膜色素上皮中维生素A的浓度最高（Bridges, 1982）。这种储存可能保护视网膜免受
Vitamin A is known to fulfil a number of physiological functions in various animal and human tissues. It is essential for the stimulation of growth and proper development of skeletal tissues, for normal reproduction, for maintenance of rod vision and, most importantly, for the preservation of the differentiated functions of mucus-secreting epithelial tissues (compare recent reviews by De Luca, 1977; Ganguly el al. 1980; Navia & Harris, 1980). Consequently, dietary lack of vitamin A leads to clinical deficiency symptoms such as growth retardation, bone malformation, degeneration of the reproductive organs, night blindness and severe alterations of epithelial structures including xerophthalmia of the conjunctiva and cornea which may result in keratomalacia and finally blindness. Metaplasia of the epithelium does, however, not only occur in the eyes but also in the epithelia of the respiratory, gastrointestinal and urogenital tracts. Histopathologically, the mucus-secreting lining of the epithelia is replaced by a stratified, squamous and keratinizing epithelium, with the exception of the intestinal mucosa which does not keratinize. Due to these broad physiological functions, vitamin A is one of the most important nutrients for the maintenance of health and life. Therefore, many biochemists have devoted a great deal of their research work to the elucidation of the mode of vitamin A action at the cellular and molecular level. Whereas the direct participation of vitamin A in the process of visual excitation is definitely established, the general molecular function of vitamin A is still being investigated and at present these investigations are strongly concentrated on the fundamental role of vitamin A in cellular differentiation. In the visual process, vitamin A plays a very special role. This was mainly shown by the brilliant research work of George Wald and his colleagues (Wald, 1968). Vitamin A, in the form of its aldehyde, retinal, is bound as a chromophore to the photosensitive pigments rhodopsin and iodopsin which are located in the outer segments of vertebrate rods and cones respectively. Whereas the cones are receptors of light of high intensity and, in the case of human cones, of colour vision, the rods are especially sensitive to light of low intensity. Vitamin A deficiency causes a decrease in the synthesis of rhodopsin and hence creates problems with dark adaptation. Several reactions including oxidation or reduction and configurational changes of the vitamin A molecule take place during the visual cycle. Vitamin A is stored as a long-chain fatty acid ester in the retina pigment epithelium which, in humans, contains the highest concentration of vitamin A apart from the liver (Bridges, 1982). This store probably protects the retina against
影响因子：
6.5
作者：
M. Brown;J. Goldstein
通讯作者：
M. Brown;J. Goldstein