A new prenyltransferase (PT) enzyme derived from the microsomal fractions of cell cultures of Morus nigra was shown to be able to prenylate exclusively chalcones with a 2′,4′-dihydroxy substitution and the isoflavone genistein. Computational studies were performed to shed some light on the relationship between the structure of the substrate and the enzymatic activity. PT requires divalent cations, particularly Mg2+, to be effective. The apparent Km values for γ,γ-dimethylallyldiphosphate and 2′,4′-dihydroxychalcone were 63 and 142 μM, respectively. The maximum activity of the enzyme was expressed during the first 10 days of cell growth. © 2003 Published by Elsevier B.V. on behalf of the Federation of European Biochemical Societies.