Cation dependent O-methyltransferases from rice
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Two lower molecular mass OMT genes (ROMT-15 and -17) were cloned from rice and expressed in Escherichia coli as glutathione S-transferase fusion proteins. ROMT-15 and -17 metabolized caffeoyl-CoA, flavones and flavonols containing two vicinal hydroxyl groups, although they exhibited different substrate specificities. The position of methylation in both luteolin and quercetin was determined to be the 3′ hydroxyl group and myricetin and tricetin were methylated not only at 3′ but also at 5′ hydroxyl groups. ROMT-15 and -17 are cation-dependent and mutation of the predicted metal binding sites resulted in the loss of the enzyme activity, indicating that the metal ion has a critical role in the enzymatic methylation.
KeywordsCaffeoyl-CoA Flavonoid O-methyltransferase Oryza sativa
Caffeoyl coenzyme A OMT
This work was supported by a grant from the Biogreen 21 Program, Rural Development Administration, Republic of Korea and partially by grant KRF-2006-005-J03401and the second Brain Korea 21 (Ministry of Education).
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