Monoterpene biosynthesis in the liverwort Conocephalum conicum: demonstration of sabinene synthase and bornyl diphosphate synthase.

(-)-Sabinene is the major monoterpene produced by a European strain of the liverwort Conocephalum conicum. A cell-free extract from in vitro cultured plants catalysed the cyclization of geranyl diphosphate to sabinene. The responsible monoterpene cyclase was partially purified and characterized as an operationally soluble enzyme of M(r) 65,000, with a pH optimum at 7.5 and a requirement for a divalent metal ion as the only cofactor, with Mg2+ preferred. The general properties of the sabinene synthase from C. conicum resemble those of other monoterpene cyclases from gymnosperms and angiosperms. A North American strain of the liverwort produces (+)-bornyl acetate as the major monoterpene and it was demonstrated that bornane-type monoterpenes are derived from geranyl diphosphate in this liverwort, as in higher plants, by the action of bornyl diphosphate synthase.