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Pathway details: quercetin glucoside biosynthesis (Arabidopsis)


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  Pathway was created on Mon Jul 29, 2013.
 Contributed by aracyc:
General background: Flavonols such as quercetin and its glycosidic derivatives (this pathway) and kaempferol/kaempferol glycoside (compare kaempferol glucoside biosynthesis (Arabidopsis)) are the major flavonoids found in Arabidopsis thaliana . Metabolic mutants of Arabidopsis were found to express a different profile of flavonols emphasizing the value of metabolic profiling for the exploration of the underlying pathways |CITS: [Graham98]|. The occurrence of the two main flavonols kaempferol and quercetin is predominant in different tissues. Quercetin appears to be the main flavonoid in seeds and kaempferol is more prominent in flowers of Arabidopsis . Beside the glycosylated monomeric flavonols, dimers and oligomers of flavonols have been identified in Arabidopsis which again accumulate in a spatially and temporally controlled manner that is dependent of seed development and maturation of seeds . The biological function of flavonoids including flavonols such as UV-protection, defense and resistance against biological and non-biological agents and interacting with plant hormones has been investigated in depth. However, flavonols also have a significant impact on human health as that they are an important component of the daily diet. Flavonols are involved in the prevention of cancer and cardiovascular diseases that have attracted researchers to reveal the causal molecular principles . About the pathway: Glycosylation is one of the most widespread modifications of plant secondary metabolites that can alter properties and functions of the modified compound. 120 putative UDP-glucose: glycosyltransferases alone have been predicted from the genome of Arabidopsis but for only a few their molecular function has been verified experimentally . The metabolic steps that generate glycosides of quercetin are catalyzed by enzymes that express broader substrate specificity and usually accept kaempferol and/or isorhamnetin to a comparable degree. In general, flavonols are preferred over flavones and flavanones matching the flavonoid composition found in Arabidopsis. The glycosyltransferases acting in Arabidopsis thaliana have been demonstrated to preferentially transport sugars to the 3-OH and 7-OH position of the C and the A-ring of the flavonol, respectively. The enzymes catalyzing the 3-O and 7-O-glucosylation have been purified from Arabidopsis |CITS: [Kim06]| . Quercetin and kaempferol-3-rhamnoside as well as their 7-O-rhamnosylated derivatives are the most abundant flavonols reported and the corresponding enzymes have been purified and characterized via functional genomic approaches just recently. The quercetin biosynthesis as displayed reflects the currently known enzymatic steps and the results of metabolic profiling .
  Parts of this pathway occur in:   cytosol     nucleus  


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