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1. (Article ID: 11945)
 
Alvarez L, Delgado G
C- and O-glycosyl-α-hydroxydihydrochalcones from Eysenhardtia polystachya
Phytochemistry 50(4) (1999) 681-687
 

Three new α-hydroxydihydrochalcones, (αR)-α,3,4,2',4'-pentahydroxydihydrochalcone, (αR)-3'-C-β-D-xylopyranosyl-α,3,4,2',4'-pentahydroxydihydrochalcone, and (αR)-3'-O-β-D-xylopyranosyl-α,3,4,2',4'-pentahydroxydihydrochalcone, together with the known coatline B [(αR)-3'-C-β-D-glucopyranosyl-α,2',3,4',4-pentahydroxydihydrochalcone], were isolated from the bark and trunks of Eysenhardtia polystachya and their structures were deduced by spectral methods. One of the isolates displayed insecticidal activity.

insecticidal activity, Leguminosae, Eysenhardtia polystachya, C- and O-glycosyl α-hydroxydihydrochalcones

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2. (Article ID: 12192)
 
Gee JM, DuPont MS, Day AJ, Plumb GW, Williamson G, Johnson IT
Intestinal transport of quercetin glycosides in rats involves both deglycosylation and interaction with the hexose transport pathway
The Journal of Nutrition 130(11) (2000) 2765-2771
 

Flavonoids are polyphenolic plant secondary metabolites with antioxidant and other biological activities potentially beneficial to health. Food-borne flavonoids occur mainly as glycosides, some of which can be absorbed in the human small intestine; however, the mechanism of uptake is uncertain. We used isolated preparations of rat small intestine to compare the uptake of the quercetin aglycone with that of some quercetin glucosides commonly found in foods, and investigated interactions between quercetin-3-glucoside and the intestinal hexose transport pathway. The nature of any metabolism of quercetin and its glucosides during small intestinal transport in vitro was determined by HPLC. The presence of quercetin-3-glucoside in the mucosal medium suppressed the uptake of labeled galactose by competitive inhibition and stimulated the efflux of preloaded galactose. Quercetin-3-glucoside and quercetin-4'-glucoside, but not quercetin-3,4'-diglucoside, were transported into everted sacs significantly more quickly than quercetin aglycone. Intact quercetin glucosides were not detected in mucosal tissue or within the serosal compartment, but both free quercetin and its metabolites were present, mainly as quercetin-3-glucuronide and quercetin-7-glucuronide. Evidently, quercetin derived from quercetin-3-glucoside passes across the small intestinal epithelium more rapidly than free quercetin aglycone. Monoglucosides of quercetin interact with the sodium-dependent glucose transporter. During passage across the epithelium, quercetin-3-glucoside is rapidly deglycosylated and then glucuronidated.

deglycosylation, quercetin glycosides, rat small intestine, sodium-dependent glucose transporter 1, flavonol uptake

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3. (Article ID: 12193)
 
Geerlings A, Ibañez MM, Memelink J, van Der Heijden R, Verpoorte R
Molecular cloning and analysis of strictosidine β-D-glucosidase, an enzyme in terpenoid indole alkaloid biosynthesis in Catharanthus roseus
Journal of Biological Chemistry 275(5) (2000) 3051-3056
 

Strictosidine β-D-glucosidase (SGD) is an enzyme involved in the biosynthesis of terpenoid indole alkaloids (TIAs) by converting strictosidine to cathenamine. The biosynthetic pathway toward strictosidine is thought to be similar in all TIA-producing plants. Somewhere downstream of strictosidine formation, however, the biosynthesis diverges to give rise to the different TIAs found. SGD may play a role in creating this biosynthetic diversity. We have studied SGD at both the molecular and enzymatic levels. Based on the homology between different plant β-glucosidases, degenerate polymerase chain reaction primers were designed and used to isolate a cDNA clone from a Catharanthus roseuscDNA library. A full-length clone gave rise to SGD activity when expressed in Saccharomyces cerevisiae. SGD shows ∼60% homology at the amino acid level to other β-glucosidases from plants and is encoded by a single-copy gene. Sgd expression is induced by methyl jasmonate with kinetics similar to those of two other genes acting prior to Sgd in TIA biosynthesis. These results show that coordinate induction of the biosynthetic genes forms at least part of the mechanism for the methyl jasmonate-induced increase in TIA production. Using a novel in vivo staining method, subcellular localization studies of SGD were performed. This showed that SGD is most likely associated with the endoplasmic reticulum, which is in accordance with the presence of a putative signal sequence, but in contrast to previous localization studies. This new insight in SGD localization has significant implications for our understanding of the complex intracellular trafficking of metabolic intermediates during TIA biosynthesis.

biosynthesis, Catharanthus roseus, strictosidine β-D-glucosidase, terpenoid indole alkaloids

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