REGULATION OF FOLATE METABOLISM

描述：(逐字摘自申请者摘要)：一个碳单位绑定到 四氢叶酸被用来从头合成嘌呤和 胸腺嘧啶和为生物提供甲基 以腺苷蛋氨酸为甲基供体的甲基化反应。这个 本研究的长期目标是研究其催化机理。 使用四氢叶酸衍生物作为辅因子的酶，并研究 一碳代谢的调节。因为一种碳的可用性 单位是限制细胞生长速度的因素之一，这些 研究与设计化疗抑制剂有关 依赖叶酸的酶。它们也与我们对 控制血浆同型半胱氨酸水平的因素是一种独立的风险 心血管疾病发生的因素。建议进行的研究 关注三种叶酸依赖酶：人亚甲基四氢叶酸 催化亚甲基四氢叶酸还原的还原酶(MTHFR) 在一个反应中将一个碳单位转化为甲基四氢叶酸 为腺苷蛋氨酸依赖的甲基化提供甲基，以及 依赖钴胺和不依赖钴胺的蛋氨酸合成酶 大肠埃希菌。蛋氨酸合成酶催化甲基转移 甲基四氢叶酸转化为同型半胱氨酸，以生产四氢叶酸和 蛋氨酸。基于对来自大肠杆菌的MTHFR的研究，已经建立了一个模型 通过叶酸的可用性来调节酶的活性的 衍生品；这一模型将测试其对监管的适用性 人类的MTHFR。钴胺依赖催化机理的研究 和来自大肠杆菌的钴胺非依赖性蛋氨酸合成酶也是 建议。这些研究将集中在激活的机制上。 甲基四氢叶酸底物，用于甲基转移和 必需锌离子在这两种酶中的催化作用，并将利用 各种各样的动力学、光谱和立体化学技术。

DESCRIPTION: (Verbatim from the Applicant's Abstract):One carbon units bound to tetrahydrofolate are utilized for the de novo biosynthesis of purines and thymidylate and for the provision of methyl groups for the biological methylation reactions that involve adenosylmethionine as the methyl donor. The long term goals of this research are to study the catalytic mechanisms of enzymes that use tetrahydrofolate derivatives as cofactors, and to study the regulation of one carbon metabolism. Because the availability of one carbon units is one of the factors that limits the rate of growth of cells, these studies are relevant to the design of chemotherapeutic inhibitors of folate-dependent enzymes. They are also relevant to our understanding of the factors that control the level of plasma homocysteine, an independent risk factor for the development of cardiovascular disease. The proposed studies focus on three folate-dependent enzymes: human methylenetetrahydrofolate reductase (MTHFR), which catalyzes the reduction of methylenetetrahydrofolate to methyltetrahydrofolate in a reaction which commits one-carbon units to provision of methyl groups for adenosylmethionine-dependent methylations, and cobalamin-dependent and cobalamin-independent methionine synthases from Escherichia coli. Methionine synthases catalyze methyl transfer from methyltetrahydrofolate to homocysteine, to produce tetrahydrofolate and methionine. Based on research with MTHFR from E. coli, a model has been developed in which enzyme activity is regulated by the availability of folate derivatives; this model will be tested for its applicability to the regulation of the human MTHFR. Studies of the catalytic mechanisms of cobalamin-dependent and cobalamin-independent methionine synthases from Escherichia coli are also proposed. These studies will focus on the mechanism of activation of the substrate, methyltetrahydrofolate, for transfer of the methyl group and on the catalytic role of the essential zinc ions in these two enzymes, and will employ a wide variety of kinetic, spectroscopic, and stereochemical techniques.