Geranyl pyrophosphate synthase

Croteau, R. and Purkett, P.T. (1989) Geranyl pyrophosphate synthase characterization of the enzyme and evidence that this chain-length specific prenyltransferase is associated with monoterpene biosynthesis in sage (Salvia officinalis). Arch. Biochem. Biophys., 271,524—35. 

This enzyme [EC 2.5.1.1] (also referred to as prenyl-transferase and geranyl-diphosphate synthase) catalyzes the reaction of dimethylallyl diphosphate and isopen-tenyl diphosphate to produce geranyl diphosphate and pyrophosphate (or, diphosphate). The enzyme will not accept larger prenyl diphosphates as substrates. 

BORNYL PYROPHOSPHATE SYNTHASE Geranyl diphosphate synthase,... 

The deuterium labelling established that the y, 5-unsaturated, nitrile 241 equilibrates at room temperature with the iV-allylketene imine 242 through an intramolecular rearrangement mechanism. Deuterium has been applied in the study of the novel palladium(0)-catalysed cyclization of 2,7-octadienyl carbonate containing an allylsilane moiety, 243, to product 244 (in 89%) and some 245 in the presence of phosphite 246 (equation 99). Intramolecular KlEs (Ah/Ad =3.0 and 3.5) have been observed in a bicyclic olefin formation (monoterpinene biosynthesis from [1- H,4- H2]- and [10- H2]-geranyl pyrophosphates) catalysed by pinene synthases from sage (Salvia officinalis). ... 

IPPP, a nucleophile (by virtue of its terminal vinyl group), and DMAPP, an electrophile, undergo condensation with elimination of pyrophosphate to yield geranyl pyrophosphate (an electrophile), which condenses with a molecule of IPPP to yield a farnesyl pyrophosphate and pyrophosphate. These reactions are probably catalyzed by the same cytosolic enzyme complex. Two molecules of farnesyl pyrophosphate and then condense head-to-head to form squalene by action of microsomal squalene synthase (Figure 19-14). 

For instance, terpene cyclases are known to catalyze the conversion of oligomeric isoprenoid pyrophosphate substrates to polycyclic hydrocarbon products. Sequence comparisons of terpene cyclases with different known specificity can allow them to be classified into monoterpene, sesquiterpene, and diterpene synthases, which utilize the 10-carbon substrate geranyl pyrophosphate, the 15-carbon substrate famesyl pyrophosphate, and the 20-carbon substrate geranyl-geranyl pyrophosphate, respectively, on the basis of sequence criteria. 

Carotenoids are usually tetraterpenoids consisting of eight isoprene units, Cj-compound. Four of the Cj units combine to yield a C o-compound, geranyl-geranyl pyrophosphate. In a tail-to-tail condensation of two these Cjq, the C40, phytoene, is formed by phytoene synthase (CrtB) whose reaction needs ATP... 

Conifers exhibit resistance to bark beetle attack and fungal invasion because of an Induced synthesis and flow of secondary resin which contains high levels of volatile monoterpenes. Monoterpene olefin synthases (geranyl pyrophosphate cyclases) were found in higher levels in fungus-infected lodgepole pine seedlings than in uninfected controls. 

In the biosynthesis of steroids lanosterol and cycloartenol, the building blocks DMAPP and IPP are first joined through famesyl diphosphate synthase to form geranyl pyrophosphate (GPP) and then to form FPP, presqualene pyrophosphate, squalene, and (S)-squalene-2,3-epoxide by corresponding enzymes, sequentially. The product (S)-squalene-2,3-epoxide is used to synthesize the sterols lanosterol (in animals) and cycloartenol (in plants) by lanosterol synthase and cycloartenol synthase, respectively [3]. Further, lanosterol and cycloartenol are converted into other steroids through steroidogenesis. 

Upon the synthesis of IPP (C5) and its isomer DMAPP (C5) by either MVA or DXP pathways, the next step is chain elongation. The carbonium ion is a potent alkylating agent that can react with IPP (three molecules of IPP converted into one molecule of geranyl diphosphate (GPP) by condensation reaction catalyzed by enzyme geranyl diphosphate synthase), to yield geranyl diphosphate (GPP). Famesyl pyrophosphate synthase (EPS) is the prenyltransferase that catalyzes l -4 condensation reactions of IPP with the allylic diphosphates, dimethylallyl diphosphate (DMAPP), to produce famesyl pyrophosphate (FPP). 

Fig. 99.1 Proposed biosynthetic pathway of artemisinin in Artemisia annua L. plant. SQS Squalene synthase, ADS amorpha-4,11-diene synthase, FPP Famesyl diphosphate, FPS Famesyl pyrophosphate synthase, GPP Geranyl diphosphate, GPPS Geranyle diphosphate synthase, GS germaciene A synthase, DMAPP Dimethylallyl diphosphate, IPP isopeniraiyl diphosphate, CPS P-caryophyllene synthase, DBR2 double bond reductase 2, ECS epi-cedrol synthase, FPP fanesyl diphosphate, PS (E)-P-famesene synthase (Drawn based on informatitm published by Abdin et al., [18] and Zhang et al., 2005)...

The initial reactions of terpene biosynthesis are catalyzed by short-chain prenyltransferases belonging to the class of trans- or cis- isoprenyl pyrophosphate synthases that catalyze chain elongation of allylic pyrophosphate substrates with IPP to generate linear polymers with defined chain length. Geranyl pyrophosphate... 

The functional isoprene units in biological systems are DMAPP and its isomer IPP. Depending on the number of isoprene subunits, one differentiates between hemi- (C5), mono- (C q), sesqui- (Cu), di- (C20), sester- (C25), tri- (Cjg), tetrater-penes (C g), and polyterpenes (Cg) (Figure 16.7). Condensation of DMAPP with IPP by geranyl-diphosphate synthase (EC 2.5.1.1) produces geranyl-pyrophosphate (GPP) as a monoterpene. Subsequent condensation of GPP with IPP by farnesyl-diphosphate synthase (EC 2.5.1.92) yields farnesyl-diphosphate... 

This enzyme [EC 2.5.1.11], also known as nonaprenyl-diphosphate synthase and solanesyl-diphosphate synthase, catalyzes the reaction of all-tra -octaprenyl diphosphate with isopentenyl diphosphate to produce all- ra 5-nonaprenyl diphosphate and pyrophosphate. The enzyme will also utilize geranyl diphosphate and di -trans-pxQny diphosphates of intermediate size as substrates, but it will not use dimethylallyl diphosphate. 

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