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The first committed step reaction of caffeine biosynthesis: 7‐methylxanthosine synthase is closely homologous to caffeine synthases in coffee ( Coffea arabica L.) 1
Author(s) -
Mizuno Kouichi,
Kato Misako,
Irino Fumi,
Yoneyama Naho,
Fujimura Tatsuhito,
Ashihara Hiroshi
Publication year - 2003
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/s0014-5793(03)00670-7
Subject(s) - caffeine , biosynthesis , biochemistry , atp synthase , methylation , enzyme , complementary dna , methyltransferase , chemistry , escherichia coli , biology , gene , endocrinology
In coffee and tea plants, caffeine is synthesized from xanthosine via a pathway that has three methylation steps. We identified and characterized the gene encoding the enzyme for the first methylation step of caffeine biosynthesis. The full‐length cDNA of coffee tentative caffeine synthase 1, CtCS1 , previously isolated by the rapid amplification of cDNA ends was translated with an Escherichia coli expression system and the resultant recombinant protein was purified using Ni‐NTA column. The protein renamed CmXRS1 has 7‐methylxanthine synthase (xanthosine: S ‐adenosyl‐ L ‐methionine methyltransferase) activity. CmXRS1 was specific for xanthosine and xanthosine 5′‐monophosphate (XMP) could not be used as a substrate. The K m value for xanthosine was 73.7 μM. CmXRS1 is homologous to coffee genes encoding enzymes for the second and third methylation steps of caffeine biosynthesis.