Nitric Oxide Reactions in Metalloenzymes

描述（由申请人提供）：本研究旨在阐明二铁蛋白中NO还原酶活性的反应中间体，最终目标是了解金属簇如何催化该反应。我们的研究将集中在三个酶：1）从Paracoccus fecans和qCuANOR从固氮芽孢杆菌，2）[血红素-铜] ba 3末端氧化酶从嗜热栖热菌，和3）解毒NO还原酶黄素蛋白A（FprA从Moorella thermoacetica）。更好地了解微生物NO还原酶是非常可取的，考虑到这些酶促反应提供了哺乳动物免疫反应的阻力。虽然这些酶中的一些存在晶体结构，但它们的NO复合物的结构和反应性尚不清楚。二铁蛋白参与解毒和还原NO还原酶反应，并被认为与NO反应形成[FeNO]2中间体。替代机械模型被认为是在这个建议和测试。共振拉曼和傅里叶变换红外光谱具有独特的能力，以确定亚硝酰中间体，并确定其NO-结合的几何形状方面的两种金属离子。新型快速冷冻淬灭（freeze-quenchment，缩写为EZQ）仪器可以在亚毫秒的时间尺度内捕获中间体，为表征以前光谱方法无法获得的反应中间体提供了新的机会。FTIR光谱，结合低温光解的N3~和CO，作为NO的替代品，提供了深入了解结合的几何形状，潜在的氢键相互作用和质子转移相关的这些NO还原酶机制。

DESCRIPTION (provided by applicant): This research aims to elucidate reaction intermediates of NO-reductase activity in diiron proteins, with the ultimate goal of understanding how the metal clusters catalyze this reaction. Our studies will focus on three enzymes: 1) denitrifying NO reductases cNOR from Paracoccus denitrificans and qCuANOR from Bacillus azotoformans, 2) the [heme-copper] ba3 terminal oxidase from Thermus thermophilus, and 3) detoxifying NO reductase flavoprotein A (FprA) from Moorella thermoacetica. A better understanding of microbial NO reductases is highly desirable considering that these enzymatic reactions provide a resistance to the mammalian immune response. Although crystal structures exist for some of these enzymes, the structure and reactivity of their NO-complexes are not known. Diiron proteins participate in both detoxifying and denitrifying NO reductase reactions and are thought to react with NO to form [FeNO]2 intermediates. Alternative mechanistic models are considered and tested in this proposal. Resonance Raman and FTIR spectroscopies have the unique capability to identify nitrosyl intermediates and to define their NO-binding geometries with regard to the two metal ions. Novel rapid freeze-quench (RFQ) instrumentation that can trap intermediates within a sub-ms timescale provides new opportunities to characterize reaction intermediates that were previously inaccessible to spectroscopic methods. FTIR spectroscopy, in conjunction with low temperature photolysis of N3~ and CO, acting as NO surrogates, offers insight into binding geometries, potential hydrogen bond interactions and proton transfers relevant to these NO reductase mechanisms.