Tyrosinase Model Complexes using Imidazole Ligands

描述（由申请人提供）：自然界中的许多蛋白质在其活性位点中含有铜，并且这些位点通常参与氧化还原催化，进行广泛的生物活性。 功能如电子载体蛋白（天青蛋白，质体蓝蛋白），加氧酶活性（酪氨酸酶， 甲烷单加氧酶、半乳糖氧化酶、细胞色素C氧化酶）和氧转运（血蓝蛋白）。具体而言，3型铜位点含有2个紧邻的铜离子，并且每个铜通过三个组氨酸氮与蛋白质骨架结合。这些3型铜中心能够可逆地结合分子氧（O2），用于分子氧运输以及有机和无机基质的氧化。在3型铜中心类别中的一种特别重要的酶是酪氨酸酶。在哺乳动物中，这种酶参与黑色素形成的生物合成途径。该酶催化羟基化，随后是酪氨酸的双电子氧化为多巴醌。鉴于酪氨酸酶的这种哺乳动物酶功能，该酶已与皮肤色素沉着异常如松弛和缺陷有关。在最近的研究中，酪氨酸酶与帕金森病和其他神经退行性疾病有关。因此，酪氨酸酶在医学、农业和工业中非常重要。由于酪氨酸酶具有重要的酶促功能，尽管其详细的反应细节仍不清楚，但已进行了大量的研究。通常，该机制被认为是通过m-h2：h2-过氧-二铜（II）物种（SP）发生的。虽然铜可以以Cu（I）、Cu（II）和Cu（III）的氧化态存在，但由于其相当积极的生物学效应，Cu（III）通常不被认为是生物学相关的。 氧化还原电位（ca. 500 mV vs. SHE），尽管这些想法先于Cu（I）胺络合物与O2的简单反应中Cu（III）的表征。最近的研究表明，底物结合诱导重排的异构体双-间-氧代-二铜（III）中间体（O）进行苯酚氧化与电子和动力学同位素参数与酶值一致。然而，本领域的这些和大多数其他研究使用了非生物相关的配体，如吡啶、吡嗪或烷基保护的咪唑。该提案旨在通过计算研究和光谱研究在模型络合物中使用更生物相关的配体来探测Cu（III）氧化态的生物相关性。铜（III）的生物相关性的这一发现将提供一个完整的范式转变铜生物化学（例如，铁（IV）-氧代中间体的非血红素铁网站）。

DESCRIPTION (provided by applicant): Many proteins in nature contain copper in their active sites, and these sites are typically involved in redox catalysis performing a wide array biological functions such as electron carrier proteins (azurin, plastocyanin), oxygenase activity (tyrosinase, methane monooxygenase, galactose oxidase, cyctochrome c oxidase), and oxygen transport (hemocyanin). Specifically, type-3 copper sites contain 2 copper ions in close proximity and each copper is bonded to the protein backbone by three histidine nitrogens. These type-3 copper centers are capable of reversibly binding dioxygen (O2) for the purposes of dioxygen transport and the oxidation of organic and inorganic substrates. One especially important enzyme in the class of type-3 copper centers is tyrosinase. In mammals, the enzyme is involved in the biosynthetic pathway for the formation of melanin. The enzyme catalyzes the hydroxylation followed by a two electron oxidation of tyrosine to dopaquinone. Given this mammalian enzymatic function for tyrosinase, the enzyme has been linked to skin pigmentation abnormalities such as flecks and defects. In recent studies, the tyrosine enzyme has been linked to Parkinson disease and other neurodegenerative disease. As such, the tyrosinase enzyme is quite significant in medicine, agriculture, and industry. Given the important enzymatic function of tyrosinase, significant study has occurred although the intimate reaction details are still unknown. Generally, the mechanism is considered to occur through a m-h2:h2- peroxo-dicopper(II) species (SP). Although copper can exist in oxidation states of Cu(I), Cu(II), and Cu(III), Cu(III) is generally not considered to be biologically relevant due to its rather positive redox potential (ca. 500 mV vs. SHE), though these ideas preceded the characterization of Cu(III) in simple reactions of Cu(I) amine complexes with O2. Recent studies have implicated a substrate-binding induced rearrangement to an isomeric bis-m-oxo-dicopper(III) intermediate (O) that performs phenol oxidation with electronic and kinetic isotope parameters consistent with enzymatic values. However, these and most other studies in the field have used non-biologically relevant ligands such as pyridine, pyrazine, or alkyl protected imidazoles. This proposal aims to use ligands more biologically relevant ligands in model complexes through computational studies and spectroscopic investigations to probe the biological relevance of the Cu(III) oxidation state. Such findings of the biological relevance of Cu(III) would provide a complete paradigm shift in copper biochemistry (e.g. Fe(IV)-oxo intermediates for non-heme iron sites).