Anthocyanin 5-aromatic acyltransferase from Gentiana triflora. Purification, characterization and its role in anthocyanin biosynthesis.

Acylation with hydroxycinnamic acids stabilizes anthocyanins and makes their colour bluer (bathochromic shift). We purified to homogeneity one acylation enzyme, hydroxycinnamoyl-CoA:anthocyanidin 3,5-diglucoside 5-O-glucoside-6"'-O-hydroxycinnamoyltransferase, from blue petals of Gentiana triflora. It is a single polypeptide protein of 52 kDa with a pI of 4.6. It catalyzes the transfer of the p-coumaric acid and caffeic acid from their CoA esters to the 5-glucosyl moiety of anthocyanidin 3,5-diglucosides but could not use malonyl-CoA as an acyl donor. Neither anthocyanidin 3-monoglucoside nor anthocyanins aromatically acylated at the 3-glucosyl moiety could be acylated by this enzyme. Aromatic acylation of anthocyanidin 3,5-diglucoside by this enzyme caused a bathochromic shift and increased pigment stability in neutral to weakly basic pH. Other anthocyanins from the petals of G. triflora were isolated and their structures were determined by fast-atom-bombardment MS and NMR. The biosynthetic pathway of gentiodelphin, a diacylated anthocyanin accumulating in G. triflora petals, is proposed on the basis of these results.