Does the malonyl-coenzyme A:21-hydroxypregnane 21-hydroxy-malonyltransferase catalyze the first step in the formation of the butenolide ring of cardenolides?

Article abstract of DOI:10.1016/0040-4039(96)00276-6

An enzyme catalyzing the transfer of the malonyl moiety from malonyl-coenzyme A 1 to the 21-hydroxy group of 3β, 14β, 21-trihydroxy-5β-pregnane-20-one 2 was isolated from Digitalis lanata leaves and characterized. The role of this particular enzyme in cardenolide biosynthesis is discussed.