Mascisch A, Rozen R
Department of Pediatrics & Biology, McGill University-Montreal Children's Hospital Research Institute, Quebec.
Somat Cell Mol Genet. 1991 Jul;17(4):391-8. doi: 10.1007/BF01233064.
MTHFD is a folate-dependent trifunctional protein comprised of three activities: N5,N10-methylenetetrahydrofolate dehydrogenase, N5,N10-methenyltetrahydrofolate cyclohydrolase, and N10-formyltetrahydrofolate synthetase. The enzymes catalyze sequential interconversion of tetrahydrofolate derivatives required for purine, methionine, and thymidylate synthesis. A Chinese hamster ovary cell line (Ade-E), reported to have reduced cyclohydrolase activity, was studied to characterize the nature of the mutation. Enzymatic assays showed reduced activities of all three enzymes of the polypeptide. Immunoblotting and immunoprecipitation of radiolabeled cell extracts indicated that MTHFD protein was greatly reduced or absent in the mutant. Northern analysis of a clonal derivative of Ade-E revealed normal levels of MTHFD mRNA. These results suggest that the mutation affects a posttranscriptional process in the synthesis of the trifunctional enzyme.
亚甲基四氢叶酸脱氢酶是一种依赖叶酸的三功能蛋白，由三种活性组成：N5,N10-亚甲基四氢叶酸脱氢酶、N5,N10-亚甲四氢叶酸环水解酶和N10-甲酰四氢叶酸合成酶。这些酶催化嘌呤、蛋氨酸和胸苷酸合成所需的四氢叶酸衍生物的顺序相互转化。对一种据报道环水解酶活性降低的中国仓鼠卵巢细胞系（Ade-E）进行了研究，以表征突变的性质。酶活性测定显示该多肽的所有三种酶的活性均降低。对放射性标记的细胞提取物进行免疫印迹和免疫沉淀表明，突变体中的亚甲基四氢叶酸脱氢酶蛋白大大减少或缺失。对Ade-E的克隆衍生物进行的Northern分析显示亚甲基四氢叶酸脱氢酶mRNA水平正常。这些结果表明该突变影响了三功能酶合成中的转录后过程。
