Detection and characterization of anS-adenosyl-l-methionine: Flavonoid 7-O-methyltransferase from leaves ofPrunus x yedoensis matsum. with special reference to prunetrin formation |
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Authors: | Nariyuki Ishikura Shinobu Nakamura Masami Mato Kazumi Yamamoto |
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Institution: | (1) Department of Biological Science, Faculty of Science, Kumamoto University, Kurokami, 860 Kumamoto, Japan |
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Abstract: | An enzyme,S-adenosyl-l-methionine: flavonoid 7-O-methyltransferase (F7OMT), catalyzing the transfer of the methyl group fromS-adenosyl-l-methionine (SAM) to the 7 position of sophoricoside (5, 7, 4′-trihydroxyisoflavone 4′-O-glucoside) and some of the other flavonoids, was detected in extracts from leaves ofPrunus x yedoensis, and it was partially purified (about 203-fold) by a combination of gel filtration and ion-exchange column chromatographies.
F7OMT was isolated as a soluble enzyme with a pH optimun of 7.5 in K-phosphate buffer. The molecular mass of F7OMT, which
had an isoelectric point at pH 4.1, was estimated by elution from a column of Sephadex G-100 to be about 36 kDa. The activity
of F7OMT was stimulated by 14 mM 2-Co2+ and reagents that react with sulfhydryl groups. The apparentKm values for sophoricoside, its aglycone genistein (5, 7, 4′-trihydroxyisoflavone) and quercetin were 1.49, 2.19 and 1.89 μM,
respectively. The apparentKm value for SAM as methyl donor was 2.08 mM. The specificity of F7OMT for methyl acceptors was not strict; flavonols, flavanones
and flavanonols in addition to isoflavones served as methyl acceptor.
An examination ofP. x yedoensis leaves during spring and autumn showed variations in the activities of F7OMT and UDP-glucose: isoflavone 4′-O-glucosyltransferase (I4′ GT). The activities of F7OMT and I4′GT increased in enlarging leaf tissues and then markedly declined
when the leaves approached maturation. In autumn leaves F7OMT activity was scarcely detected, but a small peak of I4′GT activity
was observed during autumnal reddening. |
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Keywords: | Flavonoids Isoflavone O-Methyltransferase 7-O-methylation Prunus × yedoensis Seasonal variation |
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