Flavins as Carbon Transfer Agents in Enzymology

黄酮类化合物是维生素b2的衍生物，长期以来人们都知道它可以帮助酶在生物反应中移动电子。有趣的是，现在越来越明显的是，黄素有时可以作为碳载体。有了这个奖项，化学部的生命过程化学计划正在资助密歇根大学的布鲁斯·帕勒莫博士，研究这种新认识到的、还没有很好理解的黄素反应类型。这项工作的重点是蛋白质胸苷酸合成酶控制的方式转移和修饰的一个重要的生化反应，需要DNA合成的一个碳原子。大量的细菌在合成DNA的途径中使用这种类型的反应，因此该项目正在阐明一个普遍但知之甚少的基本化学过程。该项目利用了各种化学方法，其中一些涉及先进技术，可以观察到非常快的过程。该项目的参与者，如本科生和博士后研究员，正在接受跨学科科学技术的独特融合的培训，加强我们的技术人员的能力。黄素酶化学现在远远超出了规范的边界设置的还原和氧化使用的氢当量，硫醇/二硫化物交换，单电子转移，并与O2的反应。令人惊讶的新发现是酶，使亚胺加合物与减少黄素。这些亚胺鎓加合物根据特定的酶而经历各种命运。一种黄素依赖性胸苷酸合酶（thyX）使用衍生自亚甲基四氢叶酸（CH 2 THF）的亚甲基和衍生自吡啶核苷酸的还原当量形成胸腺嘧啶。最近的证据表明，还原黄素-亚胺加合物作为碳转移剂。关键的活性中间体被捕获，它们的化学结构正在通过NMR光谱法确定。合成黄素被用来从线性自由能关系中了解关键的过渡态，并深入了解有利于碳转移而不是可能的竞争性氢化物转移的因素。质子转移，这必须是关键的控制亲电碳的转移，正在详细研究中的碳转移途径，导致胸苷酸的瞬态动力学。总的来说，该项目定义了催化策略和许多酶现在公认面临的挑战。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Flavins are derivatives of vitamin b2 that have long been known to help enzymes move electrons in biological reactions. Interestingly, it is now becoming apparent that flavins can sometimes serve as carbon-carriers. With this award, the Chemistry of Life Processes Program in the Chemistry Division is funding Dr. Bruce Palfey, University of Michigan, to investigate this newly recognized and not well understood type of reaction of flavins. This work is focusing on the way the protein thymidylate synthase controls the transfer and modification of a single carbon atom in an important biochemical reaction that is needed for DNA synthesis. A large number of bacteria use this type of reaction in the pathway to synthesize their DNA, so this project is elucidating a fundamental chemical process that is widespread but poorly understood. The project draws on a variety of chemical methods, some involving advanced technologies that allow very fast processes to be observed. The participants in the project, such as undergraduates and postdoctoral fellows, are receiving training in a unique blend of interdisciplinary scientific techniques, strengthening the capabilities of our technical workforce.Flavin enzyme-chemistry is now extending well beyond the canonical borders set by reduction and oxidation using the transfer of hydride equivalents, thiol/disulfide interchanges, single-electron transfers, and reactions with O2. Among the surprising new findings are enzymes that make iminium adducts with reduced flavins. These iminium adducts undergo a variety of fates depending on the particular enzyme. A flavin-dependent thymidylate synthase (thyX) forms thymine using a methylene derived from methylenetetrahydrofolate (CH2THF) and reducing equivalents derived from pyridine nucleotide. Recent evidence implicates the reduced flavin-iminium adduct as the carbon-transfer agent. Key reactive intermediates are being trapped and their chemical structures are being determined by NMR spectroscopy. Synthetic flavins are being used to learn about key transition states from linear free energy relationships and to gain insight into factors that favor carbon-transfer over possibly competitive hydride transfer. Proton transfers, which must be critical in controlling the transfer of electrophilic carbon, are being studied in detail by transient kinetics in the carbon-transfer route leading to thymidylate. Taken as a whole, this project is defining the catalytic strategies and challenges that many enzymes are now recognized to face.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.