A comparative density-functional study of the reaction mechanism of the O₂-dependent coproporphyrinogen III oxidase

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• 作者：Pedro J. Silva ; Maria Joã ; o Ramos
• 关键词：Coproporphyrinogen oxidase ; Mechanism ; Decarboxylation ; Minimum-energy crossing point ; Density-functional theory
• 刊名：Bioorganic and Medicinal Chemistry
• 出版年：2008
• 出版时间：15 March 2008
• 年：2008
• 卷：16
• 期：6
• 页码：2726-2733
• 全文大小：745 K

文摘

During heme biosynthesis, coproporphyrinogen III oxidase catalyzes the conversion of two propionate substituents from the highly reactive substrate coproporphyrinogen III into vinyl substituents, yielding protoporphyrinogen IX. Although the crystal structure of this important enzyme has recently been reported, the reaction mechanism of this intriguing enzyme remains the subject of intense speculation, as impairment of this enzyme has been shown to be the molecular cause behind hereditary coproporphyria. We have performed DFT calculations on model systems in order to analyze several reaction mechanisms proposed for this enzyme. The results afford a full description of the different proposals and allow the rejection of a direct electron abstraction from the protonated substrate by dioxygen. We found that O₂ addition to the (preferentially deprotonated) pyrrole substrate (yielding a hydroperoxide, which then abstracts a proton from the reactive propionate substituent) is compatible with the observed experimental reaction rate, and that the reaction may then proceed through elimination, followed by decarboxylation.