Dimethylallyl diphosphate:kaempferol 8-dimethylallyl transferase in Epimedium diphyllum cell suspension cultures.

摘要

The enzymatic formation of des-O-methylanhydroicaritin from dimethylallyl diphosphate and kaempferol was investigated in the cell-free extract of E. diphyllum cell suspension cultures. The enzyme catalysing the dimethylallyl group transfer to C-8 position of kaempferol (EC 2.5.1.) was membrane-bound and required divalent cations such as Mg2+ and Mn2+. Mg2+ was the most effective for the reaction. The enzyme showed a very broad pH optimum in the alkaline region, pH 7.5-11. It required dimethylallyldiphosphate as a sole prenyl donor, but had a rather broad substrate specificity for the prenyl acceptor. Not only kaempferol, but also quercetin (39%), apigenin (60%) and luteolin (34%) were prenylated, whereas kaempferol glycosides, naringenin and genistein, were not prenylated. It was suggested that the prenylation reaction of kaempferol precedes the glycosylation step in epimedoside A biosynthesis. The apparent Km values for dimethylallyl diphosphate and kaempferol were 0.58 and 0.13 mM, respectively.