Free polyprenols

Specifically, polyprenyl phosphate vesicles form easily, provided that their lipophilic balance (the ratio of the lipophilic part to the hydrophilic part) is adequate. Single-chain polyprenyl phosphates require at least 20 carbons (geranylgeranyl, phytyl, or phytanyl phosphates). Double-chain polyprenyl phosphates require at least two C15 (famesyl) chains to generate vesicles, although this sometimes requires the help of a small amount of the corresponding free polyprenol (Pozzi et al., 1996) (see Figure 19.7.)... 

The Css polyprenol (154) obtained from leaves of Magnolia campbelUi has been shown to be a mixture of cis- and /ran -isomers. The preparation of dolichyl phosphate (155) by a pea cell-free extract has been described. Evidence has been obtained that a lipid, containing 7V-acetylglucosamine, which was obtained from Phaseolus vulgaris hypocotyls, consists of a mixture of the dolichol (156) derivatives dolichyl pyrophosphate N-acetylglucosamine and dolichyl pyrophosphate di-N-acetylchitobiose. ... 

Polyprenols, polyprenyl alcohols acyclic, polyiso-prenoid alcohols. P. occur free or esterified with higher fatty acids in microorganisms, plants and animals. The natural source and the number of isoprene units is usually indicated in the names of P., e. g. betulapie-nol-8 is formed from 8 isoprene units and is found in Betula verrucosa. 

Dr. Luis F. Leloir, of course, is also a member of this family. He showed years ago, in 1943, his interest in fatty acid 3 oxidation. He is an uncle of the family. He showed in that year that 3 oxidation of fatty acids could be produced by a cell-free system derived from mitochondria. Much later, in 1965, he came back to the lipid field, beginning a propitious research in polyprenols in collaboration with N. Behrens, M. A. Dankert, and A. Parodi. 

Another compound of interest is dolichol which was first isolated from liver and is now known to be present in many other animal tissues. It is a long chain molecule (n=17-21), its first isoprene residue is saturated and it has 2 trans double bonds. It is found in liver part as the free alcohol and another part esteri-fied with fatty acids. We now know that a small amount is present as the phosphate or pyrophosphate and may have various sugars joined to it. These dolichol derivatives are involved in the glycosylation of proteins. An excellent review on polyprenols has been written by Hemming (1974). 

In plant tissues two major forms of polyprenols are found, e.g. free alcohols and esters with fatty acids. In some species one form is highly dominating. Similarly in animal tissues dolichols and dolichyl esters were described, accompanied by usually small amounts of dolichyl phosphate. Biological role of this latter compound is well established. Dolichyl phosphate is involved as cofactor in biosynthesis of glycoproteins and GPI-anchored proteins [3]. Biological role of free alcohol and its acyl ester has not been defined yet. As the components of biological membranes these compounds modulate membrane properties. Dolichol increases fluidity and permeability and decreases the stability of model membranes [4]. Experiments with polyprenols point to the same direction polyprenols and polyprenyl phosphates increases the fluidity and permeability of model membranes [5], Both polyprenols and dolichols could also serve as a reserve isoprenoid pool utilized by corresponding kinases. 

Polyprenols of higher plants have mostly been isolated from leaves solanesol (C45) was first obtained in 1956 from tobacco leaves. However, their occurrence in certain woody tissues has been demonstrated. Silver birch (Betula verrucosa) wood has been shown to contain fatty acid esters of betulaprenols -6 to -9 the major polyprenol, betulaprenol-7 has the structure cu-T-T-C-[C]2-C-OH (573) the poli renols from the leaves were free, and the major component had 11 isoprene units (188, 256). 

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