O-methylation of flavonoids by cell-free extracts of calamondin orange |
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Authors: | Gunter Brunet Ragai K Ibrahim |
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Institution: | Department of Biological Sciences, Concordia University, Sir George Williams Campus, Montreal, Quebec H3G 1M8, Canada |
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Abstract: | Cell-free extracts of calamondin orange (Citrus mitis) catalysed the O-methylation of almost all hydroxyls of a number of flavonoids, indicating the existence in citrus tissues of ortho, meta, para and 3-O-methyltransferases. The latter, hitherto unreported enzyme, catalysed the formation of 3-O-methyl ethers of galangin and quercetin. The stepwise O-methylation of a number of compounds, especially quercetin and quercetagetin, tends to suggest a coordinated sequence of O-methylations on the surface of a multienzyme complex. The methyl acceptor abilities of the flavonoid substrates used are discussed in relation to their hydroxyl substitution patterns and their negative electron density distribution. |
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Keywords: | Rutaceae calamondin orange flavonoids |
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