- Quercetin-4'-glucoside is more potent than quercetin-3-glucoside in protection of rat intestinal mucosa homogenates against iron ion-induced lipid peroxidation.
-
Quercetin is a typical antioxidative flavonoid found in vegetables, which is more commonly present as its glucosides, quercetin-3-glucoside (Q3G) and quercetin-4'-glucoside (Q4'G). The main aim of this study was to estimate the antioxidant activity of Q3G and Q4'G on iron ion-driven lipid peroxidation of the gastrointestinal mucosa. Q4'G markedly suppressed the lipid peroxidation when rat gastrointestinal mucosa homogenates were incubated with Fe(NO3)3 and ascorbic acid. Its effectiveness was greater as compared to that of Q3G and comparable to that of quercetin aglycone. Furthermore, Q4'G yielded higher amounts of quercetin aglycone than Q3G on incubation with the homogenates. However, Q4'G showed a lower chelating activity in comparison to Q3G. These results indicate that Q4'G, even though it has a low chelating activity, because of its efficient conversion to antioxidative aglycone on exposure to the mucosa, can act as a powerful antioxidant on iron ion driven lipid peroxidation in the intestinal mucosa. Thus, vegetables rich in Q4'G, such as onion, are likely to serve as favorable antioxidant sources for suppressing iron-induced oxidative stress in the intestinal tract.
- Murota, Kaeko,Mitsukuni, Yuki,Ichikawa, Mami,Tsushida, Tojiro,Miyamoto, Sayuri,Terao, Junji
-
-
Read Online
- Biological synthesis of isorhamnetin 3-O-glucoside using engineered glucosyltransferase
-
The gene for one of the glycosyltransferases from Populus deltoids, PGT-3, was cloned and was expressed as a glutathione S-transferase fusion protein in Escherichia coli. Various flavonoids were used as potential substrates of the purified recombinant PGT-3. Flavones having two adjacent hydroxyl groups were served as substrate. The regioselectivity of PGT-3 depends on the hydroxyl groups of the substrate. Flavones having two adjacent hydroxyl groups in the B ring were glucosylated at the 4′-hydroxyl group. However, PGT-3 transferred a glucose group to the 3-hydroxyl group of isorhamnetin. Molecular modeling and docking and site-directed mutagenesis were carried out to engineer a PGT-3 having a specificity for isorhamnetin but not for quercetin. Glu82Leu turned out to display this activity. Using the Glu82Leu mutant and a quercetin 3′- O-methyltransferase, isorhamnetin 3- O-glucoside was synthesized.
- Kim, Bong-Gyu,Sung, Su Hyun,Jung, Na Ri,Chong, Youhoon,Ahn, Joong-Hoon
-
-
Read Online
- A glycosynthase catalyst for the synthesis of flavonoid glycosides
-
Mutant exposed! The synthetic utility of glycosynthase mutant enzymes has been expanded to allow the use of lipophilic acceptors, such as flavonoids, at rates comparable with those of natural glycosyltransferases. Sequential biocatalysis allows access to both di- and monosaccharide-modifled products as well as natural product glycoflavonoids. (Figure Presented).
- Yang, Min,Davies, Gideon J.,Davis, Benjamin G.
-
-
Read Online
- Regiospecific synthesis of quercetin O-β-d-glucosylated and O-β-d-glucuronidated isomers
-
Quercetin, the polyphenolic compound, which has the highest daily intake, is well known for its protective effects against aging diseases and has received a lot of attention for this reason. Both quercetin 3-O-β-d-glucuronide and quercetin 3′-O-β-d-glucuronide are human metabolites, which, together with their regioisomers, are required for biological as well as physical chemistry studies. We present here a novel synthetic route based on the sequential and selective protections of the hydroxyl functions of quercetin allowing selective glycosylation, followed by TEMPO-mediated oxidation to the glucuronide. This methodology enabled us to synthesize the five O-β-d-glucosides and four O-β-d-glucuronides of quercetin, including the major human metabolite, quercetin 3-O-β-d-glucuronide.
- Kajjout, Mohammed,Rolando, Christian
-
p. 4731 - 4741
(2011/07/08)
-
- Cloning and functional characterisation of two regioselective flavonoid glucosyltransferases from Beta vulgaris
-
Two full-length cDNAs encoding flavonoid-specific glucosyltransferases, UGT73A4 and UGT71F1, were isolated from a cDNA library of Beta vulgaris (Amaranthaceae) cell suspension cultures. They displayed high identity to position-specific betanidin and flavonoid glucosyltransferases from Dorotheanthus bellidiformis (Aizoaceae) and to enzymes with similar substrate specificities from various plant families. The open reading frame of the sequences encode proteins of 476 (UGT73A4) and 492 (UGT71F1) amino acids with calculated molecular masses of 54.07 kDa and 54.39 kDa, and isoelectric points of 5.8 and 5.6, respectively. Both enzymes were functionally expressed in Escherichia coli as His- and GST-tagged proteins, respectively. They exhibited a broad substrate specificity, but a distinct regioselectivity, glucosylating a variety of flavonols, flavones, flavanones, and coumarins. UGT73A4 showed a preference for the 4′- and 7-OH position in the flavonoids, whereas UGT71F1 preferentially glucosylated the 3- or the 7-OH position. Glucosylation of betanidin, the aglycone of the major betacyanin, betanin, in B. vulgaris was also observed to a low extent by both enzymes. Several O-glycosylated vitexin derivatives isolated from leaves of young B. vulgaris plants and rutin obtained from B. vulgaris tissue culture are discussed as potential endogenous products of UGT73A4 and UGT71F1. The results are analyzed with regard to evolution and specificity of plant natural product glucosyltransferases.
- Isayenkova, Judith,Wray, Victor,Nimtz, Manfred,Strack, Dieter,Vogt, Thomas
-
p. 1598 - 1612
(2008/02/12)
-