EFFECT OF GYPSOGENIN 3,O-GLUCURONIDE PRETREATMENT OF GYPSOPHILA-PANICULATA AND SAPONARIA-OFFICINALIS CELL-SUSPENSION CULTURES ON THE ACTIVITIES OF MICROSOMAL 2,3-OXIDOSQUALENE CYCLOARTENOL AND AMYRIN CYCLASES

The regulation of triterpenoid saponin biosynthesis in Gypsophila paniculata and Saponaria officinalis suspension cells has been investigated by studying the effects of adding gypsogenin 3,O-glucuronide, a ubiquitous saponin precursor in plants of the genus Gypsophila which contain gypsogenin saponins, to the cultures. Treatment of suspended G. paniculata cells with gypsogenin 3,O-glucuronide 24 hr before administration of [C-14]acetate resulted in a marked reduction in the incorporation of radioactivity into saponins and their precursors but not into sterols and steryl glucosides. 2,3-Oxidosqualene-cycloartenol and -amyrin cyclase activities were measured in microsomal fractions obtained from suspension cultures of the two species. Pretreatment of cultures with gypsogenin 3,O-glucuronide was shown to lead to inhibition (in G. paniculata cells) or stimulation (in S. officinalis cells) of the 2,3-oxidosqualene-amyrin cyclase activity and was without any marked effect on 2,3-oxidosqualene-cycloartenol cyclase activity. These results strongly suggest that in these species 2,3-oxidosqualene-cyclases are regulating steps in the isoprenoid pathway orienting the biosynthetic flux towards either tetracyclic or pentacyclic triterpenes.