苯丙氨酸解氨酶(PAL,EC4.3.1.5)反应机理研究新进展

Recent advances in the research of mechanism of the Phenylalanine ammonia-lyase (PAL,EC 4.3.1.5) reaction

根据有关文献阐述了苯丙氨酸解氨酶 (PAL ,EC4 3 1 5 )反应机理研究新进展 ,主要内容包括两种反应机理的提出 :其一 ,米切尔加成反应 (MichaelAdditionReaction) ;其二 ,傅氏反应 (Friedel CraftsReaction)。通常认为该两种反应机理较好地解释了L Phe的氨消除模式 ,PAL含有的去氢丙氨酸 (DHA)单位是反应活性的关键。随着化学和分子生物学实验证据的提出 ,主要基于PAL和HAL(组氨酸解氨酶 ,EC4 3 1 3)具有高度同源性 (19%～ 2 9%序列分析 ) ,及其对“姐妹”酶HAL的X 射线结构分析 ,发现催化性的亲电试剂并非DHA ,而是 3,5 二氢 5 次甲基 4H 咪唑 4 酮 (MIO)。由此 ,提出一对非芳香L Phe异构体作探针 ,以支持这一机理的实验研究。此外 ,还列出红酵母PAL逆向催化合成非天然芳族氨基酸的相关实验结果。

Based on the survey of literature,a recent research progress of the mechanism of the Phenylalanine Ammonia Lyase (PAL,EC 4 3 1 5) reaction is described,mainly including two mechanisms proposed for this enzyme operation in its more usual elimination of ammonia mode: one relies on Michael Addition Reaction,the other relies on Friedel Crafts Reaction Generally,based on these mechanisms it is better to explain that the deamination of Phenylalanine to cinnamic acid is stereospecific and occurs with trans elimination of ammonia from the side chain carbon 2 and 3 of L Phenylalanine with the formation of the trans cinnamic acid(t CA) via PAL,and it is known that the PAL contains a dehydroalanine(DHA) unit which is the key to the reactivity According to current data from biochemistry and molecular biology,the enzymes PAL and HAL(histidine ammonia lyase, EC 4 3 1 3) have high homology(19%～29% sequence identity) The X ray structure of PAL's “sister enzyme” HAL reveals that the catalytic electrophile was not DHA but 3,5 dihydro 5 methylidene 4H imidazol 4 one(MIO) In order to provide experimental evidences for supporting the proposed mechanism,a pair of non aromatic L Phenylalanine derivatives were regarded as useful probes: one is 2,5 di hydro L Phenylalanine[3 (1,4 cyclohexadienyl) L alanine], the other is 1,4 dihydro L Phenylalanine[3 (2,5 cyclohexadienyl) L alanine] In addition, the relative experimental results for the PAL reversed biocatalytic synthesis of unnatural aromatic amino acid were made by means of bioconversion with the whole cell of Rhodotorula