Plant polyprenols

Readily available plant polyprenols from leaves of ficus (ficaprenol) or mulberry (moraprenol) are frequently used in biosynthetic studies as substitutes for bacterial undecaprenol. These polyprenols are composed of 10-12 isoprenic units (undecaprenol is the main component) with three internal E-isoprenic units localized at the carbon chain.58-59 See This Volume, pp. 341-385. 

The structures of polyprenyl diphosphate-linked intermediates of Salmonella O-specific-polysaccharide biosynthesis were confirmed by chemical synthesis of their analogs derived from the plant polyprenols ficaprenol and moraprenol (structurally related to bacterial polyprenol57) with the following study of their behavior as substrates of enzymic reactions. Synthetic polyprenyl a-D-galactopyranosyl diphosphate291,292 was found to serve as an effective acceptor for the transfer of L-rhamnosyl groups.293"295 Two synthetic, isomeric disaccharide derivatives,292 13 and296 14, were tested as acceptors for enzymic D-mannosyl transfer from GDP-Man, but only the former was found to be an efficient substrate.294... 

Table I summarizes the plant polyprenols that have been isolated and whose sources and some structural aspects have been characterized. These polyprenols occur in different species as mixtures, differing from each other in one isoprene unit. One or two members of the family are very abundant and normally account for 80% of the total polyprenol content of the plant. Most long-chain polyprenols have Z, E double bonds, the E-isoprene units being adjacent to the -residue and to a variable number of Z residues, depending on the plant (see Table I).

The polyprenols obtained from tobacco and Arum maculatum (solanesol and spadicol), which are all E, are the exceptions. Another interesting fact is that, in most seed-plants, the polyprenols are allylic, as is bacterial undecaprenol. Saturated or slightly modified polyprenols, such as animal dolichol, seem to be present only in fungi. Any of those plant polyprenols, in a phosphorylated form, can be potential sugar acceptors for transfer reactions. Experiments were performed with phosphorylated allylic polyprenols and membrane preparations from Phaseolus aureus. D-Mannose from GDP-D-mannose was incorporated into the exogenous, polyprenyl phosphates,29,49 52 but it was not possible to establish unequivocally the role of these polyprenols as lipid intermediates. 

The first evidence showing that plant polyprenols involved in glycosyl-transfer reactions are not allylic, but a-saturated, like animal dolichol (2), came from Pont Lezica and coworkers.23 The authors postulated that the presence of sugar acceptors having the properties of a-saturated polyprenyl phosphates may be a general feature of eukaryotic cells, in contrast to the a-unsaturated polyprenyl phosphates characteristic of prokaryotic cells. 

Grange and Adair73 isolated 2,3-dehydrodolichyl phosphate from in vitro studies on hen oviduct. It may be derived from 2,3-dehydrodolichyl diphosphate, a likely intermediate in the biosynthesis of dolichyl phosphate. Many questions still remain unanswered, such as is the substrate for the a-isoprene reductase, the diphosphate or the monophosphate of 2,3-dehy-drodolichol Are the unsaturated polyprenols a reserve pool for the synthesis of dolichol in plants What is the function of unsaturated, plant polyprenols How is the synthesis of saturated and unsaturated polyprenols regulated ... 

Polyprenols and dolichols Vascular plants bacteria animals +... 

Little is known as to the biosynthesis and metabolism of plant dolichols. Nevertheless, this is an interesting field if the variety of polyprenols synthesized by plants (see Table I and Scheme 1), as compared with animals, is considered. The early knowledge on the stereochemistry of E, Z-polyprenol biosynthesis was obtained by Gough and Hemming63 with a plant system. They found that the 4-5 hydrogen atom of mevalonate is retained when a Z- double bond is formed, whereas this hydrogen atom is lost in the biosynthesis of an -double bond. The same authors found similar results for rat-liver dolichol.64 With this technique, [3H]dolichol was found in rat-liver mitochondria when the animals were injected with65 4-(S)-[3H]meval-... 

Asymmetric hydrogenation of allylic alcohols (14, 39-40).1 Mammalian dol-ichols (2) are terminal dihydropolyisoprenols which are involved in glycoprotein synthesis. They contain one terminal chiral primary allylic alcohol group. The polyprenols 3 present in plants correspond to dolichols except that they lack the terminal double bond considered to be (Z). They can be obtained by hydrogenation of 2 catalyzed by (bistrifluoroacetate)ruthenium(II) and (S)-l, which affects only the terminal double bond to provide (S)-3 in >95% ee. 

The chemical structure of naturally occurring ais polyisoprenes was determined by 13C NMR spectroscopy using acyclic terpenes and polyprenols as model compounds. The arrangement of the isoprene units along the polymer chain was estimated to be in the order dimethylallyl terminal unit, three trans units, a long block of ais units, and ais isoprenyl terminal unit. This result demonstrates that the biosynthesis of cis-polyisoprenes in higher plants starts from trans,trans,trarcs-geranylgeranyl pyrophosphate. ... 

Polyisoprenoid alcohols consisting of 9 to 20 isoprene units have a widespread occurrence as indicated by their presence in the leaves of higher plants, mammalian tissues, and microorganisms. Most of the polyprenols isolated from higher plants consist of trans and cis isoprene units with the exception of solanesol, which is composed of all-trans isoprene units. The arrangement of trans and cis units in these polyprenols has been determined from a consideration of the mechanism of the formation of betula-prenols, C(30)-C(45), isolated from wood tissue of Betula verrucosa (9). However, up to the present there has been no direct evidence to prove the location of the internal trans and cis units. 

The role of undecaprenyl phosphate (C55, allylic) as a carrier of glycosyl units in the biosynthesis of bacterial cells walls is well established. Dolichyl phosphate plays a similar role in the synthesis of glycoproteins in animal systems. Evidence that prenyl lipids serve as glycosyl carriers in the biosynthesis of glycoproteins in plants is accumulating rapidly (Pont Lezica et al., 1976 Delmer al., 1978 Erickson et al., 1978). Several authors have recently reviewed the literature on the role of polyprenols as glycosyl carriers in plants (Hemming, 1978 Pont Lezica, 1979 Elbein, 1979). 

Goodwin (1977) has reviewed the general role of terpenoid lipids as membrane components in higher plants. Threlfall (1980) has recently reviewed polyprenols, terpenoid quinones and chromanols. 

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. 

Threlfall, D. R. Polyprenols and terpenoid quinones and chromanols. In Encyclopedia of Plant Physiology, New Series, Vol. 8, Secondary Plant Products (E. A. Bell, B. V. Charlwood, eds.), pp. 288-308. Springer, Berlin-Heidelberg-New York 1980 Waechter, C. J., Lennarz, W. J. The role of polyprenol-linked sugars in glycoprotein synthesis. Annu. Rev. Biochem, 45. 95-112 (1976)... 

Some of the reactions shown in.the scheme have also been detected in plants (Pont Lezica et al., 1975 Lehle et al., 1976 Brett Leloir, 1976). The polyprenol involved has been shown, by chromatography on Sephadex in deoxycholate solution to be smaller than liver in size, it has about 17 or 18 isoprene residues as compared to liver in which the compound with 19 residues is the most abundant. The compound is quite different from ficaprenol which is the major polyprenol found in plants and has 11 isoprene residues. The reactions detected in plants apparently include the formation of Dol-P-Man, Dol-P-Glc, Dol-P-P-acetylglucosamine and also some Dol-P-P-oligosaccharides. Since plants have glycoproteins of the same type found in animals it seems very likely that the scheme is also valid for them. 

They are accumulated in leaves of various plants (up to ca 5% of wet weight). Size of polyprenol molecules varies from 9 to about 100 isoprene units. It corresponds to molecular weight range from 500 to 7000. Polyprenols are stmctural analogues of natural rubber, however those described so far are smaller than low weight low weight fraction of rubber polymer. In the cell polyprenols are found as the mixture of homologues and composition of this polyprenol family is species-specific. It can serve... 

The longest polyprenols described so far were found in the representatives of Combretaceae family. HPLC records of polyprenols isolated from leaves of plants belonging to Combretaceae family are shown in Fig. 2. 

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. 

The Occurrence of Long Chain Polyprenols in Leaves of Plants. 

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