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BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

Characterization of Leachianone G 2'' -Dimethylallyltransferase, a Novel Prenyl Side-Chain Elongation Enzyme for the Formation of the Lavandulyl Group of Sophoraflavanone G in Sophora flavescens Ait. Cell Suspension Cultures

Medicinal Plant Garden, Course of Pharmaceutical Sciences, Graduate School of Biomedical Sciences, Nagasaki University, 1–14 Bunkyo-machi, 852–8521 Nagasaki, Japan (P.Z., H.Y.); Laboratory of Pharmacognosy, Gifu Pharmaceutical University, 6–1 Mitahora-higashi 5-chome, 502–8585 Gifu, Japan (K.I.); and Laboratory of Natural Product Chemistry, Course of Pharmaceutical Sciences, Graduate School of Biomedical Sciences, Nagasaki University, 1–14 Bunkyo-machi, 852–8521 Nagasaki, Japan (I.K.)

Leachianone G (LG) 2''-dimethylallyltransferase, a novel prenyl side-chain elongation enzyme, was identified in Sophora flavescens Ait. cultured cells. The enzyme transfers a dimethylallyl group to the 2'' position of another dimethylallyl group attached at position 8 of LG to form sophoraflavanone G, a branched monoterpenoid-conjugated flavanone characteristic to this plant. This membrane-bound dimethylallyltransferase required Mg²⁺ (optimum concentration was 10 mM) for the reaction and had an optimum pH of 8.8. It utilized dimethylallyl diphosphate as the sole prenyl donor, and the 2'-hydroxy function in LG was indispensable to the activity. The apparent K_m values for dimethylallyl diphosphate and LG were 59 and 2.3 µM, respectively. Subcellular localization of three enzymes that participated in the formation of the lavandulyl group was also investigated by sucrose density gradient centrifugation. Two prenyltransferases, naringenin 8-dimethylallyltransferase and LG 2''-dimethylallyltransferase, were localized in the plastids, whereas 8-dimethylallylnaringenin 2'-hydroxylase, which catalyzes the crucial step in the lavandulyl-group formation, was associated with the endoplasmic reticulum. These results suggest the close cooperation between the plastids and the endoplasmic reticulum in the formation of lavandulyl groups.

¹ Present address: Faculty of Life Sciences, Toyo University, 1–1–1 Izumino, 374–0193 Itakura, Japan.

^* Corresponding author: e-mail yamamoto{at}itakura.toyo.ac.jp; fax 81–276–82–9206.

Received April 9, 2003; returned for revision June 5, 2003; accepted July 31, 2003.

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