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The glycosylation and deglycosylation of cardiac glycosides was investigated using cell suspension cultures and shoot cultures, both established from Digitalis lanata EHRH. plants, as well as isolated enzymes. Shoots were capable of glucosylating digitoxigenin, evatromonoside, digiproside, glucodigitoxigenin and digitoxin. Suspension cultured Digitalis cells glucosylated all the substrates mentioned but digiproside, whereas the UDP-glucosedependent cardenolide glucosyltransferase isolated from that source did not accept digitoxigenin and digiproside as substrates. It is concluded that at least three different glucosyltransferases are involved in cardiac glycoside formation in Digitalis. Similar experiments carried out with glucosylated cardenolides which were administered to cultured cells, shoots and a cardenolide/~-glucosidase isolated from young leaves revealed that at least two different glucosidases occur in Digitalis lanata, albeit in different tissues or during different phases of development. The biotransformation of glucoevatromonoside was investigated using unlabelled compound and [lac-glucose]glucoevatromonoside synthesized enzymatically. After 7 d of incubation almost no radioactivity could be recovered from the cardenolide fraction, indicating that the terminal glucose of glucoevatromonoside was now incorporated into volatile, hydrophilic and insoluble compounds. Since, on the other hand, large amounts of cardenolides were found in the experiments with unlabelled glucoevatromonoside it is assumed that steady state or pool size regulation is achieved by the coordinated action of a cardenolide glucosidase and a glucosyltransferase.Abbreviations: Acdox -D-acetyldigitoxose, dgen-digoxigenin, dox-D-digitoxose, dten -digitoxigenin, dtl -Ddigitalose, fuc-D-fucose, gten-gitoxigenin, qun-D-quinovose, CGH-cardenolide 16'-O-glucohydrolase, DFT -UDP-fucose:digitoxigenin 3-O-fucosyltransferase, DGT-UDP-glucose:Digitoxin 16'-O-glucosyltransferase, DQT -UDP-quinovose:digitoxigenin 3-O-quinovosyltransferase

Posters found to be present in biosynthetically active Digitalis tissues (4). Therefore, the fate of the glucose moiety of 2 might be traced in feeding experiments with [14C-glucose]-glucoevatromonoside. Enzymatic synthesis of labeled 2 was performed with a partially purified digitoxin glucosyltransferase (5) using [14C-glucosei-UDPG (31.6nmol; 37OkBq) and evatromonoside (1.2pmol) as the substrates. After 3h of incubation 55% of the radioactivity apphed was found in 2 which was separated from unconverted 1 and 14C-labeled UDPG by column chromatography on silica gel RP-8 using acetonitrile-water mixtures for step gradient elution. The purity of synthesized 2 was confirmed by TLC.