Bassan Arianna, Borowski Tomasz, Schofield Christopher J, Siegbahn Per E M
Department of Physics, Stockholm Center for Physics, Astronomy and Biotechnology, Stockholm University, 10691 Stockholm, Sweden.
Chemistry. 2006 Nov 24;12(34):8835-46. doi: 10.1002/chem.200501459.
The reaction catalyzed by the plant enzyme 1-aminocyclopropane-1-carboxylic acid oxidase (ACCO) was investigated by using hybrid density functional theory. ACCO belongs to the non-heme iron(II) enzyme superfamily and carries out the bicarbonate-dependent two-electron oxidation of its substrate ACC (1-aminocyclopropane-1-carboxylic acid) concomitant with the reduction of dioxygen and oxidation of a reducing agent probably ascorbate. The reaction gives ethylene, CO(2), cyanide and two water molecules. A model including the mononuclear iron complex with ACC in the first coordination sphere was used to study the details of O-O bond cleavage and cyclopropane ring opening. Calculations imply that this unusual and complex reaction is triggered by a hydrogen atom abstraction step generating a radical on the amino nitrogen of ACC. Subsequently, cyclopropane ring opening followed by O-O bond heterolysis leads to a very reactive iron(IV)-oxo intermediate, which decomposes to ethylene and cyanoformate with very low energy barriers. The reaction is assisted by bicarbonate located in the second coordination sphere of the metal.
利用杂化密度泛函理论研究了植物酶1-氨基环丙烷-1-羧酸氧化酶（ACCO）催化的反应。ACCO属于非血红素铁（II）酶超家族，可在依赖碳酸氢盐的情况下对其底物ACC（1-氨基环丙烷-1-羧酸）进行双电子氧化，同时伴随氧气的还原以及可能是抗坏血酸的还原剂的氧化。该反应生成乙烯、二氧化碳、氰化物和两个水分子。使用了一个在第一配位层中包含与ACC的单核铁配合物的模型来研究O - O键断裂和环丙烷环开环的细节。计算表明，这个不寻常且复杂的反应是由一个氢原子提取步骤引发的，该步骤在ACC的氨基氮上产生一个自由基。随后，环丙烷环开环，接着是O - O键的异裂，生成一个反应性很强的铁（IV）-氧中间体，该中间体以非常低的能垒分解为乙烯和氰基甲酸酯。该反应由位于金属第二配位层的碳酸氢盐辅助。
