Ethylene biosynthesis: processing of a substrate analog supports a radical mechanism for the ethylene-forming enzyme

被引:24
作者
Pirrung, MC [1 ]
Cao, J [1 ]
Chen, JL [1 ]
机构
[1] Duke Univ, PM Gross Chem Lab, Dept Chem, Durham, NC 27708 USA
来源
CHEMISTRY & BIOLOGY | 1998年 / 5卷 / 01期
关键词
1-aminocyclobutanecarboxuylate; biosynthesis; ethylene; hydroxylation; radical;
D O I
10.1016/S1074-5521(98)90086-2
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
Background: The chemical mechanism of the final step of ethylene biosynthesis (the conversion of 1-aminocyclopropanecarboxylic acid, ACC, to ethylene by ACC oxidase, the ethylene-forming enzyme, EFE) is poorly understood. Two possibilities have been suggested: a radical mechanism and an N-hydroxylation mechanism. We investigated reaction pathways available to radical intermediates in this reaction using an ACC analog, 1-aminocyclobutanecarboxylic acid (ACBC) as a substrate. Results: ACBC was converted to dehydroproline (Delta(1)-pyrroline-2-carboxylic acid) by the EFE via a ring expansion process. The possibility that an N-hydroxyaminoacid (produced during two-electron oxidation) acts as an intermediate in this process was eliminated by control experiments. Chemical model reactions involving two-electron oxidants, such as a positive halogen (X+), which presumably generate N-halo derivatives, produce only decarboxylation products. Radical-based oxidants, in contrast, generate dehydroproline. Model reactions involving sequential single-electron transfer mechanisms also produce dehydroproline; thus our results support the proposal that the EFE-catalyzed step of ethylene biosynthesis proceeds using a radical-based mechanism. Conclusions: Our results provide support for a radical mechanism in the final step of ethylene biosynthesis and refute an alternative N-hydroxylation mechanism. This work extends the idea that the intrinsic chemical reactivity of a high energy iron-ore intermediate can account for the observed products in ethylene biosynthesis.
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页码:49 / 57
页数:9
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