?5-3?-hydroxysteroid dehydrogenase/?5-?4-ketosteroid isomerase (3?-HSD), a possible enzyme of cardiac glycoside biosynthesis, in cell cultures and plants of Digitalis lanata EHRH

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Abstract
The in vitro transformation of pregnenolone into progesterone in Digitalis lanata tissues was shown to be catalyzed by a 3β-hydroxysteroid dehydrogenase/ketosteroid isomerase (3β-HSD). Product formation was monitored by HPLC. The enzyme could be partially characterized and 3β-HSD activities were measured in various Digitalis lanata tissues and in cell cultures of other plant species. Since no correlation was observed between biosynthetic competence of the tissue and 3β-HSD activity, it was concluded that this enzyme does not play a major role in regulating cardenolide biosynthesis.