title: Ethylene biosynthesis by 1-aminocyclopropane-1-carboxylic acid oxidase: a DFT study.
abstract: 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.
authors.affiliation: Department of Physics, Stockholm Center for Physics, Astronomy and Biotechnology, Stockholm University, 10691 Stockholm, Sweden. arianna@physto.se
authors.forename: Arianna
authors.initials: A
authors.lastname: Bassan
authors.forename: Tomasz
authors.initials: T
authors.lastname: Borowski
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Schofield
authors.forename: Per E M
authors.initials: PE
authors.lastname: Siegbahn
mesh_terms: D000594:Amino Acid Oxidoreductases / Q000737:chemistry / Q000378:metabolism*; D001639:Bicarbonates / Q000737:chemistry / Q000378:metabolism; D001665:Binding Sites; D002245:Carbon Dioxide / Q000737:chemistry / Q000378:metabolism; D002384:Catalysis; D003486:Cyanides / Q000737:chemistry / Q000378:metabolism; D003521:Cyclopropanes / Q000737:chemistry; D005030:Ethylenes / Q000096:biosynthesis*; D006859:Hydrogen / Q000737:chemistry; D007501:Iron / Q000737:chemistry / Q000378:metabolism; D008433:Mathematics; D008968:Molecular Conformation; D009584:Nitrogen / Q000737:chemistry; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D014867:Water / Q000737:chemistry / Q000378:metabolism
chemical_list: D001639:Bicarbonates; D003486:Cyanides; D003521:Cyclopropanes; D005030:Ethylenes; D014867:Water; D002245:Carbon Dioxide; D006859:Hydrogen; C030797:cyclopropane; D007501:Iron; D000594:Amino Acid Oxidoreductases; C059460:1-aminocyclopropane-1-carboxylic acid oxidase; D009584:Nitrogen; D010100:Oxygen