Bassan Arianna, Blomberg Margareta R A, Siegbahn Per E M
Department of Physics, Stockholm Center for Physics, Astronomy and Biotechnology, Stockholm University, 106 91, Stockholm, Sweden.
Chemistry. 2003 Jan 3;9(1):106-15. doi: 10.1002/chem.200390006.
The reaction mechanism for the formation of the hydroxylating intermediate in aromatic amino acid hydroxylases (i.e., phenylalanine hydroxylase, tyrosine hydroxylase, tryptophan hydroxylase) was investigated by means of hybrid density functional theory. These enzymes use molecular oxygen to hydroxylate both the tetrahydrobiopterin cofactor and the aromatic amino acid. A mechanism is proposed in which dioxygen forms a bridging bond between the cofactor and iron. The product is an iron(II)-peroxy-pterin intermediate, and iron was found to be essential for the catalysis of this step. No stable intermediates involving a pterin radical cation and a superoxide ion O(2)(-) were found on the reaction pathway. Heterolysis of the O-O bond in the iron(II)-peroxy-pterin intermediate is promoted by one of the water molecules coordinated to iron and releases hydroxypterin and the high-valent iron oxo species Fe(IV)=O, which can carry out subsequent hydroxylation of aromatic rings. In the proposed mechanism, the formation of the bridging C-O bond is rate-limiting in the formation of Fe(IV)=O.
通过杂化密度泛函理论研究了芳香族氨基酸羟化酶（即苯丙氨酸羟化酶、酪氨酸羟化酶、色氨酸羟化酶）中羟化中间体形成的反应机制。这些酶利用分子氧对四氢生物蝶呤辅因子和芳香族氨基酸进行羟化。提出了一种机制，其中双氧在辅因子和铁之间形成桥连键。产物是铁（II）-过氧蝶呤中间体，并且发现铁对于该步骤的催化至关重要。在反应途径上未发现涉及蝶呤自由基阳离子和超氧离子O₂⁻的稳定中间体。与铁配位的一个水分子促进了铁（II）-过氧蝶呤中间体中O-O键的异裂，释放出羟基蝶呤和高价铁氧物种Fe（IV）=O，其可对芳香环进行后续羟化。在所提出的机制中，桥连C-O键的形成在Fe（IV）=O的形成中是限速的。
