Heme/Copper and Heme/Nonheme Iron O(2) and NO Reactivity

描述（由申请人提供）：长期研究目标是设计、合成和研究模型化合物系统，这些系统可以帮助阐明与血红素-铜氧化酶（HCOs）、一氧化氮还原酶（NORs）和相关蛋白质利用的二氧（O2）和氮氧化物（NOx）化学相关的结构、金属连接、光谱学和反应性的基本方面。HCOs和NOR是进化上相关的酶，在需氧和厌氧生物体内的细胞过程中发挥关键作用。它们共同具有血红素/M（M = Cu或非血红素Fe）活性位点，其分别还原裂解O2或NO。提出的研究将有助于更好地了解酶的结构和机制，提供了一个全面的和基本的基础相关的生物处理的O2，NO和亚硝酸盐（NO2-），甚至超出血红素和铜金属蛋白领域。具体目标包括（1）血红素/Cu-O 2加合物的表征，新的质子化和低自旋衍生物，以及它们的（结构）和电子/成键性质的阐明，（2）由血红素-过氧-Cu络合物系统促进的还原性O-O断裂的研究，特别是新的低自旋化合物，其中改变铜配体环境和血红素轴向“碱”配体是方法的一部分。系统变化的还原剂和酸将在调查中，以阐明这些因素的关键，这一过程，包括在化学或生物化学系统中的“氧活化”的一个关键方面，（3）就业和研究的配体系统，具有铜配体咪唑-苯酚部分，诱导O-O还原裂解化学为相应的血红素/铜-O2组装。此外，两个化学系统设计，以测试如何CcO（生物）化学导致的铜配体的组氨酸-酪氨酸交联的实际形成，将详细研究。(4)调查与输入变化的血红素轴向'基地'配体的化学系统，其中血红素/NO/O2的配位化学将研究与过氧亚硝酸盐的形成和随后的反应机理。这种化学反应发生在NO双加氧酶（NOD）中，这些酶与细胞NO稳态密切相关，并可能通过氨基酸硝化化学作用参与细胞信号传导。(5)研究 与NOR、血红素/Cu组装相关的化学，其能够实现NO还原偶联。一个明确的重点将是推定的hypontrite中间体，它们的结构和它们的反应性，导致N2 O和H2O产品的形成机制。这些信息是理解N-N偶联和N-O裂解化学的关键，它们也与质子化偶联。这些过程也是广泛的利益与其他生物金属酶氮氧化物处理。这一目标还包括努力阐明血红素/铜介导的亚硝酸盐还原为NO和互补的NO氧化为亚硝酸盐的化学。在手血红素/铜组件使这种化学和进一步的机械探测是必要的;这些过程是至关重要的NO信号和连接到细胞响应[O2]浓度的变化。

DESCRIPTION (provided by applicant): The long-term research objective is to design, synthesize and investigate model compound systems which can help elucidate fundamental aspects of structure, metal-ligation, spectroscopy and reactivity relevant to the dioxygen (O2) and nitrogen oxide (NOx) chemistry utilized by heme-copper oxidases (HCOs), nitric oxide reductases (NORs) and related proteins. HCOs and NOR's are evolutionarily related enzymes which play critical roles in cellular processes within aerobic and anaerobic organisms. They have in common a heme/M (M = Cu or non-heme Fe) active site that reductively cleaves O2 or NO, respectively. The research proposed will contribute to a better understanding of enzyme structure and mechanism by providing a comprehensive and fundamental basis relevant to biological processing of O2, NO and nitrite (NO2-), that extends even beyond the heme and Cu metalloprotein sphere. Specific aims include (1) the characterization of heme/Cu- O2 adducts, new protonated and low-spin derivatives and elucidation of their (structures) and electronic/bonding properties, (2) the study of reductive O-O cleavage promoted by heme-peroxo-Cu complex systems, especially new low-spin compounds where altering the copper-ligand environment and heme axial 'base' ligands is a part of the approach. Systematically varied reducing agents and acids will be employed in the investigations in order to elucidate those factors crucial for this process, comprising a critical aspect of 'oxygen activation' in chemical or biochemical systems, (3) the employment and study of ligand systems which possess a copper-ligand imidazole-phenol moiety which induces O-O reductive cleavage chemistry for a corresponding heme/copper-O2 assembly. Also, two chemical systems designed to test how CcO (bio)chemistry leads to the actual formation of the copper-ligand His-Tyr crosslink, will be studied in detail. (4) investigation of a chemical system with input variations f the heme axial 'base' ligand, where heme/NO/O2 coordination chemistry will be studied mechanistically with regard to peroxynitrite formation and its subsequent reactivity. This chemistry occurs in NO dioxygenases (NODs), enzymes critically involved in cellular NO homeostasis and possibly in cellular signaling via amino-acid nitration chemistry. (5) the study of chemistry relevant to NORs, heme/Cu assemblies that enable NO reductive coupling. A clear focus will be on the mechanism of formation of putative hypontrite intermediates, their structures and their reactivity leading to N2O and H2O products. Such information is key to the understanding of N-N coupling and N-O cleavage chemistries which are also coupled to protonation. These processes are also of broad interest with respect to other biological metalloenzyme nitrogen oxide processing. This aim also includes efforts to elucidate the chemistry of heme/Cu mediated nitrite reduction to NO and complementary NO oxidation to nitrite. In-hand heme/Cu assemblies enable this chemistry and further mechanistic probing is necessary; these processes are critical to NO signaling and linked to cellular responses to changes in [O2] concentrations.