Hashidoko Y, Tahara S
Faculty of Agriculture, Hokkaido University, Kita-ku, Sapporo, 060-8589, Japan.
Arch Biochem Biophys. 1998 Nov 15;359(2):225-30. doi: 10.1006/abbi.1998.0911.
The stereochemical specificity in the decarboxylation of E-4-hydroxycinnamic acid catalyzed by E-4-hydroxycinnamate decarboxylase (4-HCD) of Klebsiella oxytoca was investigated. Unlike the pyrolytic decarboxylation of 8-deuterated E-4-hydroxycinnamic acid to yield an equimolecular mixture of 8-Z- and 8-E-deuterated 4-hydroxystyrenes, treating 8-deuterated E-4-hydroxycinnamic acid with the enzyme in H2O-based buffer yielded 8-Z-deuterated 4-hydroxystyrene selectively. The specific E-orientation in catalysis and the substrate specificity requiring 4-OH in the substrates suggest that decarboxylation by K. oxytoca 4-HCD occurs via a para-quinone methide intermediate. Stereoselective protonation and the liberation of CO2 by an intermediary molecule are most likely the key reaction steps in the stereochemical specificity of the newly incorporated hydrogen.
研究了产酸克雷伯菌的E-4-羟基肉桂酸脱羧酶（4-HCD）催化E-4-羟基肉桂酸脱羧反应中的立体化学特异性。与8-氘代E-4-羟基肉桂酸热解脱羧生成8-Z-和8-E-氘代4-羟基苯乙烯的等分子混合物不同，在基于H2O的缓冲液中用该酶处理8-氘代E-4-羟基肉桂酸可选择性地生成8-Z-氘代4-羟基苯乙烯。催化过程中特定的E-取向以及底物中需要4-OH的底物特异性表明，产酸克雷伯菌4-HCD的脱羧反应是通过对-醌甲基化物中间体进行的。立体选择性质子化以及中间分子释放CO2很可能是新掺入氢的立体化学特异性中的关键反应步骤。
