Poly-prenyl pyrophosphate

Membrane preparations from immature stages of the fruit fly Ceratitis capitata catalyse the transfer of o-mannose into lipid-linked oligosaccharides. The lipid-linked trisaccharide has been partially characterized and tentatively assigned the structure D-mannosyl -> NN diacetylchitobiosyl-poly(prenyl-pyrophosphate). These insect poly(prenyl)-oligosaccharides may participate in glycoprotein biosynthesis. 

All ra 5-polyprenols are believed to be formed from GFPP by the chain extension process already discussed (Sect. 8.1.1.2), followed by hydrolysis by appropriate phosphatases. There is evidence to show that synthesis of all- raAi -poly-prenol pyrophosphates occurs in mitochondrial membranes and chloroplasts. Biosynthetic studies have shown that c/5, ra 5-polyprenols are synthesized from FPP or GGPP by cw-prenylation by IIP (189, 369, 392). 

Chain elongation during polymerization of prenyl units can be terminated in one of a number of ways. The pyrophosphate group may be hydrolyzed to a monophosphate or to a free alcohol. Alternatively, two polyprenyl compounds may join "head to head" to form a symmetric dimer. The C30 terpene squalene, the precursor to cholesterol, arises in this way from two molecules of famesyl diphosphate as does phy-toene, precursor of the Qo carotenoids, from E,E,E geranylgeranyl diphosphate. The phytanyl groups of archaebacterial lipids (p. 385) arise rather directly from geranylgeranyl diphosphate by transfer of the poly-... 

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