Ethylene biosynthesis by 1-aminocyclopropane-1-carboxylic acid oxidase: a DFT study |
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Authors: | Bassan Arianna Borowski Tomasz Schofield Christopher J Siegbahn Per E M |
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Institution: | Department of Physics, Stockholm Center for Physics, Astronomy and Biotechnology, Stockholm University, 10691 Stockholm, Sweden. arianna@physto.se |
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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. |
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Keywords: | density functional calculations ethylene nonheme iron enzymes reaction mechanisms |
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