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首页> 外文OA文献 >Two Tropinone Reductases with Distinct Stereospecificities from Cultured Roots of Hyoscyamus niger1
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Two Tropinone Reductases with Distinct Stereospecificities from Cultured Roots of Hyoscyamus niger1

机译：从Hyscyamus niger1的培养根中具有不同立体特异性的两种Tropinone还原酶。

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摘要

Tropinone is an alkamine intermediate at the branch point of biosynthetic pathways leading to various tropane alkaloids. Two stereospecifically distinct NADPH-dependent oxidoreductases, TR-I and TR-II, which, respectively, reduce tropinone to 3α-hydroxytropane (tropine) and 3β-hydroxytropane (ψ-tropine), were detected mainly in the root of tropane alkaloid-producing plants but not in nonproducing cultured root. Both reductases were purified to near homogeneity from cultured root of Hyoscyamus niger and characterized. The TR-I reaction was reversible, whereas the TR-II reaction was essentially irreversible, reduction of the ketone being highly favored over oxidation of the alcohol ψ-tropine. Marked differences were found between the two reductase in their affinities for tropinone substrate and in the effects of amino acid modification reagents. Some differences in substrate specificity were apparent. For example, N-propyl-4-piperidone was reduced by TR-II but not by TR-I. Conversely, 3-quinuclidinone and 8-thiabicyclo[3,2,1]octane-3-one were accepted as substrates by TR-I but hardly at all by TR-II. Both enzymes were shown to be class B oxidoreductases, which transfer the pro-S hydrogen of NAD(P)H to their substrates. Possible roles of these tropinone reductases in alkaloid biosynthesis are discussed.
机译：Tropinone是生物合成途径分支点上的烷胺中间体，可导致各种托烷生物碱。主要在产生托烷生物碱的根中检测到两种立体特异性的NADPH依赖的氧化还原酶TR-1和TR-II，它们分别将肌钙蛋白还原为3α-羟托烷（tropine）和3β-羟托烷（ψ-tropine）。植物，但不在非生产的培养根中。两种还原酶均从黑潮草的根部纯化至接近同质并进行了表征。 TR-I反应是可逆的，而TR-II反应基本上是不可逆的，与醇-托品醇的氧化相比，酮的还原是非常有利的。发现两种还原酶之间在肌钙蛋白底物的亲和力和氨基酸修饰试剂的作用上存在明显差异。底物特异性的一些差异是显而易见的。例如，N-丙基-4-哌啶酮被TR-II还原但未被TR-1还原。相反，TR-I接受3-奎宁环酮和8-噻二环[3,2,1]辛烷-3-酮作为底物，而TR-II几乎不接受。两种酶均显示为B类氧化还原酶，可将NAD（P）H的pro-S氢转移至其底物。讨论了这些肌钙蛋白还原酶在生物碱生物合成中的可能作用。

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