Studies on the Biosynthesis of Cardiac Glycosides: Fucosyltransferase Activity in Leaves ofDigitalis lanata

Abstract

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.

Transcriptome and Metabolite analysis reveal candidate genes of the cardiac glycoside biosynthetic pathway from Calotropis procera

“…Formation of this intermediate molecule is supposed to be derived from mevalonic acid via triterpenoid and phytosterols intermediate. Predominance of either terpenoid pathway precursors (MVA or MEP pathway) in synthesis of cardenolide intermediate is not clear yet 55 56 . Total 47 unigenes related to terpenoid backbone biosynthesis were annotated from the transcriptome data.…”

Glycosylation in cardenolide biosynthesis

“…Any investigations of the enzymatic steps in cardenolide glycoside formation are limited by the unavailability of putative co-substrates of the respective glycosyltransferases. In an attempt to elucidate the fucosylation of digitoxigenin on the enzyme level we recently synthesized UDP-a-D-fucose by condensing a-Dfucopyranosyl phosphate and commercial uridine 5'monophosphomorpholidate (Faust et al 1992b). A partially purified enzyme from young leaves of Digitalis lanata EHRH.…”

“…When partially purified enzyme preparations were used, the incubation time and protein concentration were adapted in such way that at least 70% of the cardenolide substrate was left (DQT) were assayed as described by Faust et al (1992b).…”

“…Digiproside was synthesized from digitoxigenin and 2,3,4-tri-O-acetyl-a-D-fucopyranosyl bromide as described previously (Faust et al 1992b). Lanatoside A, digitalinum verum, glucoverodoxin, odorobioside G and/3-methyldigitoxin, which was used as the internal cardenolide standard, were from Boehringer Mannheim (Mannheim, Germany).…”