期刊
PLANT JOURNAL
卷 36, 期 6, 页码 808-819出版社
BLACKWELL PUBLISHING LTD
DOI: 10.1046/j.1365-313X.2003.01928.x
关键词
(R,S)-reticuline 7-O-methyltransferase; norcoclaurine 6-O-methyltransferase; alkaloid biosynthesis; opium poppy; Papaver somniferum
S-Adenosyl-L-methionine:(R,S)-reticuline 7-O-methyltransferase converts reticuline to laudanine in tetrahydrobenzylisoquinoline biosynthesis in the opium poppy Papaver somniferum. This enzyme activity has not yet been detected in plants. A proteomic analysis of P. somniferum latex identified a gel spot that contained a protein(s) whose partial amino acid sequences were homologous to those of plant O-methyltransferases. cDNA was amplified from P. somniferum RNA by reverse transcription PCR using primers based on these internal amino acid sequences. Recombinant protein was then expressed in Spodoptera frugiperda Sf9 cells in a baculovirus expression vector. Steady-state kinetic measurements with one heterologously expressed enzyme and mass spectrometric analysis of the enzymatic products suggested that this unusual enzyme is capable of carrying through sequential O-methylations on the isoquinoline and on the benzyl moiety of several substrates. The tetrahydrobenzylisoquinolines (R)-reticuline (4.2 sec(-1) mM(-1)), (S)-reticuline (4.5 sec(-1) mM(-1)), (R)-protosinomenine (1.7 sec(-1) mM(-1)), and (R,S)-isoorientaline (1.4 sec(-1) mM(-1)) as well as guaiacol (5.9 sec(-1) mM(-1)) and isovanillic acid (1.2 sec(-1) mM(-1)) are O-methylated by the enzyme with the ratio k(cat)/K (m) shown in parentheses. A P. somniferum cDNA encoding (R,S)-norcoclaurine 6-O-methyltransferase was similarly isolated and characterized. This enzyme was less permissive, methylating only (R,S)-norcoclaurine (7.4 sec(-1) mM(-1)), (R)-norprotosinomenine (4.1 sec(-1) mM(-1)), (S)-norprotosinomenine (4.0 sec(-1) mM(-1)) and (R,S)-isoorientaline (1.0 sec(-1) mM(-1)). A phylogenetic comparison of the amino acid sequences of these O-methyltransferases to those from 28 other plant species suggests that these enzymes group more closely to isoquinoline biosynthetic O-methyltransferases from Coptis japonica than to those from Thalictrum tuberosum that can O-methylate both alkaloid and phenylpropanoid substrates.
作者
我是这篇论文的作者
点击您的名字以认领此论文并将其添加到您的个人资料中。
推荐
暂无数据