Smirnoff Nicholas, Conklin Patricia L, Loewus Frank A
School of Biological Sciences, University of Exeter, Hatherly Laboratories, Prince of Wales Road, Exeter, EX4 4PS, United Kingdom; e-mail:
Annu Rev Plant Physiol Plant Mol Biol. 2001 Jun;52:437-467. doi: 10.1146/annurev.arplant.52.1.437.
The structure of the familiar antioxidant L-ascorbic acid (vitamin C) was described in 1933 yet remarkably, its biosynthesis in plants remained elusive until only recently. It became clear from radioisotopic labeling studies in the 1950s that plant ascorbic acid biosynthesis does not proceed in toto via a route similar to that in mammals. The description in 1996 of an Arabidopsis thaliana mutant deficient in ascorbic acid prompted renewed research effort in this area, and subsequently in 1998 a new pathway was discovered that is backed by strong biochemical and molecular genetic evidence. This pathway proceeds through the intermediates GDP-D-mannose, L-galactose, and L-galactono-1,4-lactone. Much research has focused on the properties of the terminal enzyme responsible for conversion of the aldonolactone to ascorbate, and on related enzymes in both mammals and fungi. Two of the plant biosynthetic genes have been studied at the molecular level and additional ascorbate-deficient A. thaliana mutants may hold the key to other proteins involved in plant ascorbate metabolism. An analysis of the biosynthesis of ascorbate and its analogues in algae and fungi as well as the study of alternative proposed pathways should broaden our understanding of ascorbate metabolism in plants. With a biosynthetic pathway in hand, research on areas such as the control of ascorbate biosynthesis and the physiological roles of ascorbate should progress rapidly.
常见的抗氧化剂L-抗坏血酸（维生素C）的结构于1933年被阐明，但值得注意的是，直到最近其在植物中的生物合成仍不清楚。从20世纪50年代的放射性同位素标记研究中可以清楚地看出，植物抗坏血酸的生物合成并非完全通过与哺乳动物相似的途径进行。1996年对一种缺乏抗坏血酸的拟南芥突变体的描述促使该领域重新展开研究，随后在1998年发现了一条新途径，该途径有强有力的生化和分子遗传学证据支持。这条途径通过GDP-D-甘露糖、L-半乳糖和L-半乳糖-1,4-内酯等中间体进行。许多研究集中在负责将醛糖内酯转化为抗坏血酸的末端酶的特性，以及哺乳动物和真菌中的相关酶。已经在分子水平上研究了两个植物生物合成基因，其他缺乏抗坏血酸的拟南芥突变体可能是参与植物抗坏血酸代谢的其他蛋白质的关键。对藻类和真菌中抗坏血酸及其类似物生物合成的分析以及对其他提出的途径的研究，应该会拓宽我们对植物抗坏血酸代谢的理解。有了生物合成途径，抗坏血酸生物合成的控制和抗坏血酸的生理作用等领域的研究应该会迅速取得进展。
