text: 光裂合酶。由系統發生學來看，光裂合酶是一個相當古老的酵素，從細菌、真菌，到動物體內都有，且在植物體內尤為重要。人類等胎盤哺乳類體內則並無此酵素活性，而是使用另一種較無效率的核苷酸切除修復法來取代光裂合酶。DNA中相鄰的胸腺嘧啶受到紫外線的照射時，會形成共價鍵，形成環丁烷橋，稱為胸腺嘧啶二聚體。形成胸腺嘧啶二聚體的基因會導致基因在複製和轉錄時出現錯誤。光裂合酶會接在DNA上，切除胸腺嘧啶二聚體，並修復回原本的樣子。光裂合酶為一種黃素蛋白，內含兩個捕光性輔因子。所有的光裂合酶都含有FADH−，並可根據他的第二輔因子分為兩類。第一類為葉酸性光裂合酶，其第二輔因子的成分為次甲基四氫葉酸蝶呤。FAD本身即有酵素活性，第二輔因子則可在低光狀態下加速反應進行。被光活化的光裂合酶會將FADH−的電子，轉移給胸腺嘧啶二聚體來裂解二聚體。除了第二輔因子之外，光裂合酶也可根據序列相似性分為兩種，第一種主要在革蘭氏陰性菌、陽性菌、嗜鹽古菌、真菌，和植物體內。Proteins containing this domain also include "Arabidopsis thaliana" s 1 and 2, which are blue light photoreceptors that mediate blue light-induced gene expression and modulation of circadian rhythms.、可以將光裂合酶分為兩類。The first class contains enzymes from Gram-negative and Gram-positive bacteria, the halophilic archaebacteria Halobacterium halobium,以及真菌與植物。阿拉伯芥的 1與2亦含有此種結構域，作為促進藍光基因表現與調整晝夜節律的光受體。The second class are named cryptochrome (Cry), found in species as diverse as Drosophila, Arabidopsis, Synechocystis, and Human (Cry-DASH). These were previously assumed to have no DNA repair activity because of negligible activity on double-stranded DNA. A study by A. Sancar and P. Selby provided evidence to suggest this branch of cryptochromes have photolyase activity with a high degree of specificity for cyclobutane pyrimidine dimers in single-stranded DNA. Their study showed that VcCry1 from "Vibrio cholerae", X1Cry from "Xenopus laevis", and AtCry3 from "Arabidopsis thaliana" all had photolyase activity on UV irradiated ssDNA in vitro.有些防曬油含有此酵素，宣稱可以治癒紫外線曬傷。
metadata.dataset: erhwenkuo/wikipedia-zhtw
metadata.title: 光裂合酶
metadata.url: https://zh.wikipedia.org/wiki?curid=4681714