AGLYCONE AND GLYCOSIDE SPECIFICITY OF APPLE SKIN FLAVONOID GLYCOSYLTRANSFERASE

O-Glycosyltransferase(s) extracted from apple (Malus pumila Mill) frui t skin showed activity towards a range of flavonols and anthocyanins. However, no glycosylating activity was shown towards a dihyroflavonol (dihydroquercetin), a flavanone (eriodictyol) or a flavone (luteolin). The enzyme preparation glycosylated those flavonoids normally present in apple skins (quercetin and cyanidin) and in addition several other related compounds (delphinidin, fisetin, isorhamnetin, kaempferol, my ricetin and pelargonidin). This enzyme(s) specifically transferred the glycosyl moiety from sugar nucleotide donors to the 3-position of the flavonoid nucleus. Only flavonoid 3-glycosides occur naturally in app le skin. Activity with different sugar donors was in the order galacto se > glucose > xylose, which reflected the ratios of cyanidin and quer cetin glycosides found in apple fruit skin. There were slight differen ces in the relative UFGT activity with quercetin and the three differe nt sugar donors between 'Granny Smith' and 'Splendour', and this was r eflected by similar differences in the ratios of endogenous quercetin glycosides.