Glycosylation and Acylation

An enzyme which will catalyse the glycosylation of anthocyanidin has yet to be described, but one which will do this for flavonols has been found in several plants. In an earlier communication, Larson pointed out that maize pollen is a particularly rich source of a glucosyltransferase capable of converting kaempferol and quercetin to their 3-glucosides. The enzyme has now been extracted with distilled water and purified four-fold by (NH4 2S04 fractionation. It has a requirement for UDP-glucose, mercaptoethanol, and Ca and possesses an optimum pH of 8.2. The for quercetin was found to be 0.6 X 10- moir . 

The mechanism of biosynthesis of flavone C-glycosidcs still remains obscure, but an isomerase which will convert isovitexin (39) into vitexin (40) has recently been detected in the Reporter s laboratory. It occurs in the grass Briza media, which contains glycoflavones, and it operates in only the one direction, the pH optimum being about 6.8. 

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Post-translation modification Changes that occur to proteins after peptide-bond formation has occurred, e.g. glycosylation and acylation. 

The pKj, value (2.43) of the hydration constant of the cyanidin was found to be lower than the pKj, values of glycosylated and acylated cyanidins, meaning lower resistance of the anthocyanidin to hydration. The stability of nonacylated 3,5-diglucosides was lower compared to the 3-glucoside because the 5 position markedly lowered the hydration constant due to decreased electron density of the pyrilium ring that favors nucleophilic attack by water, enhancing hemiacetal formation. ... 

Schwinn, K.E. et al.. Expression of an Antirrhinum majus UDP-glucose flavonoid-3-0-glucosyltransferase transgene alters flavonoid glycosylation and acylation in lisianthus (Eustoma grandiflorum Grise.). Plant ScL, 125, 53, 1997. 

C-NMR chemical shifts of isolated phenylethanoid glycosides were shown in Table 2. At present, two dimensional NMR spectra, such as - H COSY), 1H-13C(HMQC and HMBC) directly afford the importnat structural information Chemical shifts by methylation, glycosylation and acylation suggested the information of substituted carbon positions. 

Flavonoids are a large group of polyphenolic compounds that occur commonly in plants. This group contains more than 8000 known compounds, and this number is constantly growing because of the great structural diversity arising from the various hydroxylation, methoxylation, glycosylation, and acylation patterns. 

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