The aldo-keto reductase (AKR) superfamily comprises proteins that catalyse mainly the reduction of carbonyl groups or carbon–carbon double bonds of a wide variety of substrates including steroids. Such types of reactions have been proposed to occur in the biosynthetic pathway of the cardiac glycosides produced by Digitalis plants. Two cDNAs encoding leaf-specific AKR proteins (DpAR1 and DpAR2) were isolated from a D. purpurea cDNA library using the rat D4-3-ketosteroid 5b-reductase clone.
