- Purification and characterization of coclaurine N-methyltransferase from cultured Coptis japonica cells
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S-Adenosyl-L-methionine (SAM): coclaurine N-methyltransferase (CNMT), which catalyzes the transfer of a methyl group from S-adenosyl-L-methionine to the amino group of the tetrahydrobenzylisoquinoline alkaloid coclaurine, was purified 340-fold from Coptis japonica cells in 1% yield to give an almost homogeneous protein. The purified enzyme, which occurred as a homotetramer with a native Mr of 160 kDa (gel-filtration chromatography) and a subunit Mr of 45 kDa (SDS-polyacrylamide gel electrophoresis), had an optimum pH of 7.0 and a pI of 4.2. Whereas (R)-coclaurine was the best substrate for enzyme activity, Coptis CNMT had broad substrate specificity and no stereospecificity; CNMT methylated norlaudanosoline, 6,7-dimethoxyl-1,2,3,4-tetrahydroisoquinoline and 1-methyl-6,7-dihydroxy-1,2,3,4,-tetrahydroisoquinoline. The enzyme did not require any metal ion. p-Chloromercuribenzoate and iodoacetamide did not inhibit CNMT activity, but the addition of Co2+, Cu2+ or Mn2+ at 5 mM severely inhibited such activity by 75, 47 and 57%, respectively. The substrate-saturation kinetics of CNMT for norreticuline and SAM were of the typical Michaelis-Menten-type with respective Km values of 0.38 and 0.65 mM.
- Choi, Kum-Boo,Morishige, Takashi,Sato, Fumihiko
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p. 649 - 655
(2007/10/03)
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- Biosynthesis. Part 24. Speculative Incorporation Experiments with 1-Benzylisoquinolines and a Logical Approach via C6-C2 and C6-C3 Precursors to the Biosynthesis of Hasubanonine and Protostephanine
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Many possible 1-benzyltetrahydroisoquinolines have been examined as possible advanced precursors of the alkaloids hasubanonine (1) and protostephanine (2) in Stephania japonica plants, but none was incorporated significantly.Administration of various precursor molecules having only one aromatic ring, such as tyrosine, has demonstrated that both alkaloids are derived from two different C6-C2 biogenetic units.The subsequent failure of further 1-benzyltetrahydroisoquinolines and bisphenethylamines to be incorporated suggested the intermediacy of either (a) modified 1-benzylisoquinolines or (b) trioxygenated C6-C2 building blocks.Precursors designed to examine the first possibility, such as 1-benzyl-3,4-dihydroisoquinolines or 1-benzyl-1-carboxytetrahydroisoquinolines, were not incorporated into (1) and (2) whereas two 3',4',5'-trioxygenated 2-phenylethylamines were incorporated.These findings allow further delineation of the requirements for later precursors of the alkaloids (1) and (2).
- Battersby, Alan R.,Jones, Raymond C. F.,Kazlauskas, Rymantas,Thornber, Craig W.,Ruchirawat, Somsak,Staunton, James
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p. 2016 - 2029
(2007/10/02)
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