Monoterpene synthases, multiple

The tremendous diversity of volatile monot-erpenes, sesquiterpenes and diterpenes arises from enzymatic modification of the non-volatile prenyl diphosphate intermediates GPP, FPP and GGPP through the action of terpene synthases (TPS) [57, 58], many of which have the distinctive ability to catalyze the formation of multiple products from a single prenyl diphosphate snb-strate [59-61]. A recently isolated monoterpene synthase from Nicotiana suaveolens flowers was found to produce a blend of 5 cyclic and 2 acyclic monoterpenes, all of which are components of N. suaveolens floral scent [62]. In Arabidopsis, two terpene synthases account for the biosynthesis of nearly all sesquiterpenes found in the floral volatile blend [63]. In addition to sesquiterpenes, Arabidopsis flowers also emit monoterpenes dominated by P-myrcene and (5)-linalool. While P-myrcene could likely be synthesized by multi-product monoterpene synthases [64, 65], one single-product monoterpene synthase may be solely responsible for the emission of (5)-linalool [65]. In snapdragon, two specialized single-product monoterpene synthases are responsible for the biosynthesis of the two floral monoterpenes, myrcene and ( )-P-ocimene [66]. The reaction mechanism of TPSs involves the formation of carbocationic intermediates which can then be differentially metabolized to form multiple products [57, 58]. 

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