Iridoid Biosynthesis: 7-Deoxyloganetic Acid 1-O-Glucosyltransferase in Cultured Lonicera japonica Cells

• Published in: Plant Biotechnology 2002, Vol.19(5), pp.295-301
• Main Authors: YAMAMOTO, Hirobumi, SHA, Manyoung, KITAMURA, Yoshie, YAMAGUCHI, Misako, KATANO, Nobuyuki, INOUE, Kenichiro
• Format: Article
• Language: English
• Subjects: 7-Deoxyloganetic acid; Biosynthesis; Caprifoliaceae; Cell suspension cultures; Enzyme; Hydrangea; Iridoid glucoside; Loganin; Lonicera japonica; UDP-glucose: iridoid 1-O-glucosyltransferase
• ISSN: 1342-4580; 1347-6114
• DOI: 10.5511/plantbiotechnology.19.295

Iridoid 1-O-glucosylation enzyme activities of crude cell-free extracts prepared from loganin-producing plants and nonproducing cultured cells were comparatively examined. Crude cell-free extracts from Lonicera japonica cell suspension cultures glucosylated 7-deoxyloganetic acid, 7-deoxyloganetin, and loganetin, but not iridotrial, an intermediate just preceding 7-deoxyloganetic acid. Crude cell-free extracts from Hydrangea macrophylla young leaves also glucosylated 7-deoxyloganetin and loganetin, whereas those from cultured cells induced from iridoid-nonproducing plants did not show any iridoid glucosylation activity. The partially purified glucosyltransferase from L. japonica cells showed the highest glucosylation activity for loganetin. However, kinetic studies showed that Km values for 7-deoxyloganetic acid, 7-deoxyloganetin, and loganetin were 106μM, 561μM, and 660μM, respectively, indicating that the enzyme had the highest affinity to 7-deoxyloganetic acid. These data suggest the presence of a pathway for the biosynthesis of loganin, in which 7-deoxyloganetic acid is glucosylated at the 1-O position to give 7-deoxyloganic acid, which is further hydroxylated and methylated to produce loganin.