CELLULAR-ORGANIZATION OF CARDENOLIDE BIOTRANSFORMATION IN DIGITALIS-GRANDIFLORA MILL

The cellular compartmentalization of cardenolide biotransformation in Digitalis grandiflora Mill. cell cultures was investigated. The presen ce of UDP-glucose: digitoxin 16'-O-glucosyltransferase (DGT; EC 2.4.1. -), acetyl-CoA: digitoxin 15'-O-acetyltransferase (DAT; EC 2.3.1.-) an d cardenolide 16'-O-glucohydrolase (CGH; EC 3.2.1.21) was demonstrated and their time courses during one cell culture cycle were established . The activities of DGT, DAT and CGH were quite constant over time and leveled off at around 3, 30 and 100 mukat, respectively, per kg prote in. The cardenolide products formed by DGT action were shown to be exc lusively localized in the central vacuole. The cellular distributions of DGT, CGH and unspecific beta-glucosidase were investigated and it w as shown that DGT and CGH are not localized in the vacuoles, whereas u nspecific glucosidase is. The influence on cardenolide uptake of the s et of biotransformation enzymes present in a given cell line is discus sed. An updated cellular model of cardenolide biotransformation is pro posed.