Identification, Properties and Genetic Control of UDP-ʟ-Rhamnose: Anthocyanidin 3-O-Glucoside, 6″-O-Rhamnosyltransferase Isolated from Retals of the Red Campion (Silene dioica)

An enzyme catalyzing the transfer of the rhamnosyl moiety of UDP-ʟ-rhamnose to the 6 -hydroxyl group of the 3-O-bound glucose of anthocyanidin 3-O-glucosides has been demonstrated in petal extracts of Silene dioica plants. The enzyme activity is controlled by a single dominant gene N; no rhamnosyltransferase activity is found in petals of n/n plants. The 60-fold purified rhamno-syltransferase exhibits a pH optimum of 8.1, has a molecular weight of about 45000 daltons, is stimulated by the divalent metal ions Mg2+, Mn2+ and Co2+, and has a “true Km” value of 0.09 mᴍ for UDP-ʟ-rhamnose and 2.2 mᴍ for cyanidin 3-O-glucoside. Pelargonidin 3-O-glucoside and delphinidin 3-O-glucoside can also serve as acceptor. The enzyme can also catalyze the rhamnosylation of anthocyanidin 3,5-diglucosides although at reduced rate. The biosynthetic pathway for the synthesis of cyanidin 3-rhamnosylglucoside-5-glucoside in petals of S. dioica is discussed.

Anthocyanins Isolated from Petals of Various Genotypes of the Red Campion (Silene dioica (L.) Clairv.)

Anthocyanin pigments present in petals of various genotypes of Silene dioica were identified by RF-values, UV-spectra, partial and total hydrolysis, alkalysis, NMR-and IR-spectra. Both the 3-glucosides, 3,5-diglucosides, 3-rutinosides and 3-rutinosides-5-glucosides of cyanidin and pelargonidin were found. The location of the acyl group at the 3-O-bound sugar in acylated anthocyanins - p-coumaric acid in pelargonidin-glycosides and caffeic acid in cyanidin-glycosides - has been determined by partial hydrolysis, peroxide oxidation, and oxidative cleavage with sodium periodate followed by reduction with sodium borohydride and identification of the polyalcohols formed after hydrolysis. The phenolic acids have been shown to be attached to the 4-hydroxyl group of rhamnose in anthocyanidin 3-rhamnosylglucosides and to the 6-hydroxyl group of the 3-O -bound glucose in anthocyanidin 3-O-glucosides.