Mode of Substrate Interaction and Energetics of Carbon-Oxygen Bond Formation of the Dopamine -Monooxygenase Reaction

详细信息    查看全文

• 作者：Kandatege Wimalasena and Kevin R. Alliston
• 刊名：Biochemistry
• 出版年：1999
• 出版时间：November 9, 1999
• 年：1999
• 卷：38
• 期：45
• 页码：14916 - 14926
• 全文大小：186K
• 年卷期：v.38,no.45(November 9, 1999)
• ISSN：1520-4995

文摘

Previous studies have shown that the dopamine -monooxygenase (DM; E.C. 1.14.17.1)/1-(2-aminoethyl)-1,4-cyclohexadiene (CHDEA) reaction partitions between side chain and ring H-abstractionto produce the side-chain-hydroxylated product, 2-amino-1-(1,4-cyclohexadienyl)ethanol, and the aromatizedproduct, phenylethylamine, and that the two pathways do not crossover. [Wimalasena, K., and May, S.W. (1989) J. Am. Chem. Soc. 111, 2729-2731; Wimalasena, K., and Alliston, K. R. (1995) J. Am. Chem.Soc. 117, 1220-1224]. We now report that the ring H-abstraction pathway of the reaction further partitionsto produce the ring hydroxylated product, CHDEA-6OH, and the aromatized product, PEA, at the carbon-oxygen bond formation step. The ring hydroxylation is shown to be stereospecific, exclusively producingthe (S) product. The absolute stereospecificity of the ring and side-chain hydroxylations of the DM/CHDEA reaction suggests that the side-chain pro-R hydrogen of the enzyme-bound substrate is close toperpendicular to the aromatic ring of the phenylethylamine substrate or cyclohexadiene ring of CHDEA.The relative activation energy parameters suggest that the partitioning of the ring H abstraction pathwaybetween aromatized and ring hydroxylated products is due to the partitioning of the high-energyintermediates, the cyclohexadienyl radical and the Cu(II)-O species, between carbon-oxygen bondformation and direct electron transfer. The relatively high activation enthalpic favorability and entropicunfavorability for the carbon-oxygen bond formation strongly suggest that the critical balancing of thesetwo opposing forces is mandatory for the desired product formation.