MAMMALIAN HEME PEROXIDASE ACTIVE SITE REACTIVITY

描述：(改编自申请者摘要)哺乳动物血红素过氧化物酶 酶分布在各种组织中，但常见的反应性 特点是利用过氧化氢氧化卤化物或 拟卤化物离子。白细胞和外分泌液中的过氧化物酶 产生氧化卤化物或假卤化物物种作为防御机制 对抗入侵的微生物。白细胞髓过氧化物酶的氯化物氧化 离子也可能与炎症反应有关，这种氧化反应 过程被认为与动脉粥样硬化的形成有关。外分泌液过氧化物酶 如乳过氧化物利用硫氰酸根离子作为生理活性物质 底物。直到最近，才确定了血红素的结构 髓过氧化物酶和乳过氧化物酶。这些建筑是前所未有的 血红素化合物，其中常见的1-和5-位甲基 原卟啉IX转化为羟甲基，这些部分 被酯化为蛋白质的谷氨酸和天冬氨酸残基。这个 髓过氧化物酶的X-射线结构显示与 在蛋氨酸残基和蛋白质之间形成硫离子的蛋白质 卟啉的2位乙烯基团。基本的反应性 这些不寻常的血红素物种的特性如何值得研究 卟啉取代基可以决定酶的催化性能，并且还 就已知的自杀底物对哺乳动物过氧化物酶的抑制而言。 为实现这一长期目标而制定的具体目标包括 如下：(1)金属卟啉配合物的化学合成 含有羟甲基或乙烯基硫离子取代基，以 包括从乳过氧化物酶中分离的血红素的全合成；(2) 合成化合物的物理表征，特别要注意 取代基对氧化还原电位的影响，以及取代基对氧化还原电位的影响 硫离子与氯离子氧化成键的存在 髓过氧化物酶；(3)人工合成的 乳酸过氧化物酶的化合物和血红素多肽对自杀的修饰作用 基材，具有相应的改性的结构表征 以及(4)不寻常的血红素结构与 一种独特的、可能具有抗菌作用的氧化硫氰酸盐中间体。

DESCRIPTION: (adapted from applicant's abstract) Mammalian heme peroxidase enzymes are distributed in various tissues, but the common reactivity feature is utilization of hydrogen peroxide for oxidation of halide or pseudo-halide ions. Peroxidases in leucocytes and in the exocrine fluids generate oxidized halide or pseudo-halide species as a defense mechanism against invading microbes. Leucocyte myeloperoxidase oxidation of chloride ion may also be associated with an inflammatory response, and this oxidative process has been implicated in atherogenesis. Exocrine fluid peroxidases such as lactoperoxidas utilize thiocyanate ion as the physiological substrate. Only very recently hav the heme structures been identified for myeloperoxidase and lactoperoxidase. The structures are unprecedented for heme compounds, in that the 1- and 5-position methyl groups of the common protoporphyrin IX are converted to hydroxymethyl groups, and these moieties are esterified to glutamate and aspartate residues of the protein. The X-ray structure of myeloperoxidase reveals a third covalent linkage to the protein with sulfonium ion formation between a methionine residue and the 2-position vinyl group of the porphyrin. The fundamental reactivity properties of these unusual heme species merit investigation in terms of how the porphyrin substituents may dictate enzyme catalytic properties, and also in terms of known suicide substrate inhibition of the mammalian peroxidases. The specific objectives directed toward this long-term goal include the following: (1) chemical synthesis of metalloporphyrin complexes that contain either the hydroxymethyl or the vinyl sulfonium ion substituents, to include total synthesis of the heme isolated from lactoperoxidase; (2) physical characterization of the synthetic compounds with particular regard to substituents effects on redox potentials, and a correlation of the presence of the sulfonium ion linkage with chloride ion oxidation by myeloperoxidase; (3) investigation of the susceptibility of the synthetic compounds and the heme peptides of lactoperoxidase to modification b suicide substrates, with corresponding structural characterization of modified hemes; and (4) correlation of the unusual heme structures with formation of a unique, presumably antimicrobial oxidized thiocyanate intermediate.