Enzymatic A-ring hydroxylation of flavonols in position 8

Project number: Research project P 13020 Project title: Encymatic A-Ring Hydroxylation of Flavonols in Position 8 ABSTRACT OF THE PROJECT Yellow flavonols, such as gossypetin and quercetagetin, and their derivatives, owe their bright yellow colour to the presence of a hydroxy1 or methoxyl group in position 6 - or 8 of the aromatic A-ring in addition to the basic 5,7- hydroxylation pattern. In some plants these compounds contribute to flower colouration. During the last twenty years considerable progress has been made in the elucidation of the biosynthesis of flavonoids, but enzymatic hydroxylation in positions 6 and 8 of ring A has not been detected so far. In a preliminary experiment we were able to show that incubation of ( 14C) - quercetin with the microsomal fraction of Chrysanthemum segetum cv. "Prado" in the presence of NADPH leads to the formation of ( 14C) - gossypetin (8- hydroxyquercetin). This new hydroxylating activity will be studied in detail in the present project. The biochemical investigations are an essential precondition for the subsequent molecular biological studies which include the isolation of a flavonol 8-hydroxylase full-size cDNA clone. The project contributes to several interesting subjects: (i) elucidation of an up to now unknown step of the flavonoid biosynthesis. (ii) This also gives important information about the nature of the involved enzyme belonging most probably to the group of cytochrome P450 - dependent monooxygenases, which have increasingly importance during the last few years. (iii) Furthermore, this enzyme will provide us with a tool leading to novel yellow-coloured varieties of ornamental plants through the creation of new transgenic plants.