Isopentenyl pyrophosphate, polyprenol

Polyterpenoids.—The presence of dolichols (202) with up to 23 isoprene units, in various sources, has been reported.In addition to these dolichols, which have their terminal isoprene unit saturated, fully unsaturated polyprenols have been found. Bovine pituitary contains a mixture of cis-trans-isomers of decaprenol (203), a Cioo prenol from bovine thyroid has been shown by n.m.r. to have eighteen cis- and two frans-isoprene residues, and 2,3-dehydrodoli-chyl pyrophosphate (204) has been identified as a product of a chick enzyme system and isopentenyl pyrophosphate.The structure of ulmoprenol from Eucommia ulmoides has been elucidated (207). ... 

This alignment of the trans and cis units clearly indicates that these polyprenols are synthesized in vivo by the cis addition of isopentenyl pyrophosphate to trans,trans,trems-geranylgeranyl pyrophosphate (10). 

Dolichol phosphate, which is a crucial intermediate, has been shown to be synthesised in a variety of tissues and subcellular fractions, of which mitochondrial outer membranes are especially active. These are also a major store of dolichol. The synthesis can start from isopentenyl pyrophosphate or its precursor, mevalonic acid (see the reviews of Beytia and Porter, 1976 Daleo and Pont-Lezica, 1977 Daleo etaiy 1977). In one case the product was the a-unsaturated polyprenol phosphate (dehydrodolichol phosphate), which suggests that a-saturation may occur after phosphorylation, at least in tissues such as hen oviduct (Grange and Adair, 1977 Adair and Keller, 1982). 

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