The characterization and distribution of hexahydropolyprenyl esters in cultures of Aspergillus fumigatus Fresenius

Enzymatic cyclization of all-trans pentaprenyl and hexaprenyl methyl ethers by a cell-free system from the protozoon Tetrahymena pyriformis. The biosynthesis of scalarane and polycyclohexaprenyl derivatives

A cell-free system from the protozoon Tetrahymena pyriformis capable of cyclizing squalene into tetrahymanol cyclizes all-trans pentaprenyl methyl ether to a scalarane-type sesterterpene and all-trans hexaprenyl methyl ether to bicyclo-, tricyclo-, tetracyclo- and pentacyclohexaprenyl methyl ethers, each corresponding to a possible cationic intermediate. The structures of the cyclization products have been determined by spectroscopic methods and are compatible with a biogenetic scheme involving polyprenyl ether cyclization. This is the first direct proof of an enzymatic cyclization of higher isoprenic alcohol derivatives, and we assume it was performed by the squalene-to-hopane cyclase of the protozoon. The formation of a scalarane-type sesterterpene from C25 polyprenyl methyl ether suggests that these terpenoids, whose presence is restricted to a few sponges, might be in fact microbial metabolites. Tricyclopolyprenyl derivatives have been identified in the organic matter from numerous sediments and they were interpreted as being chemical fossils of still unidentified microorganisms. The cyclization of hexaprenyl methyl ether is the first attempt of identification of these tricyclopolyprenol derivatives in living organisms.

Identification and characterization of dolichyl dolichoate, a novel isoprenoic derivative in bovine thyroid

Inspection of the TLC pattern of the neutral lipid fraction of bovine thyroid reveals, in addition to cholesteryl esters and dolichyl fatty acid esters, the presence of a not yet identified compound in the most apolar lipid region. This unknown compound was purified on a preparative scale by silicic acid column chromatography, Lipidex-5000 gel-filtration chromatography and preparative thin-layer chromatography. By chemical (hydrolysis and reduction) and spectroscopic (ultraviolet, infrared, NMR, mass spectroscopy) methods this lipid was identified as dolichyl dolichoate. The homologue pattern was analyzed, by HPLC and FDMS, respectively.

Distribution, metabolism and function of dolichol and polyprenols

Polyisoprenoid alcohols consisting of 9 or more isoprene units are present in all living cells. They can be fully unsaturated (polyprenols) or alpha-saturated (dolichol). Dolichol forms may have additional saturation at or near the omega-end. Some species contain ony dolichol or only polyprenols while others have nearly equal amounts of both types. Some polyisoprenoid alcohols consist entirely of trans isoprene units but most, including dolichol, contain both trans and cis units. Considerable advances in lipid methodology have occurred since the first review of polyisoprenoid alcohols by Hemming in 1974. For example, direct analysis of both dolichol and Dol-P by HPLC has replaced earlier methods which were often both insensitive and inaccurate. The availability of radiolabeled dolichol and polyprenols has facilitated studies concerning the metabolism and distribution of these compounds. Those studies suggest that only a small portion of the dolichol present in cells is likely to be involved in glycosylation. Polyisoprenoid alcohols are usually present at a family of homologues where each differs in size by one isoprene unit. Little or no size related specificity has been observed for any reaction involving dolichol or polyisoprenol intermediates. The overall length of polyisoprenoid alcohols may, however, affect the manner in which these compounds influence the physical and biochemical properties of membranes. Studies on the biosynthetic pathway leading from cis, trans Pol-PP by phosphatase action. The formation of the dolichol backbone from a polyprenol requires the action of an additional enzyme, an alpha-saturase. This enzyme does not always act at the level of a single common substrate, since Pol-PP, Pol-P, and polyprenol all appear to be utilized as substrates. The major product of the de novo pathway differs among different species. Dol-P would appear to be the most energy efficient end-product since it can participate directly in glycoprotein formation. Most often, however, Dol-P is not the major product of metabolic labeling experiments. In some cases, dolichol is formed so that rephosphorylation is required to provide Dol-P for participation in glycoprotein formation. The kinase responsible for this phosphorylation appears to bypass the considerable stores of dolichol present in tissues (i.e. sea urchin eggs) in favor of dolichol derived directly from de novo synthesis. Although HMGR is a major regulatory component of the pathway leading to polyisoprenoid alcohols and cholesterol, control is most often not co-ordinated.(ABSTRACT TRUNCATED AT 400 WORDS)

Studies on isoprenoid biosynthesis with bacterial intact cells

For the study on the regulation of isoprenoid biosynthesis with intact cells, some strains of bacteria capable of growing on mevalonate as a sole carbon source were isolated from soil. Many of them incorporated [14C]-mevalonate, [14C]isopentenyl- and [14C]farnesyl pyrophosphates into the cells. However, radioactivity was found in their degradation products but not in isoprenoids. Addition of [14C]isopentenyl pyrophosphate, farnesyl pyrophosphate and Mg2+ ions in combination to the culture of a strain of Arthrobacter gave rise to 14C-incorporation into isoprenoids. Radioactivity was found in polyprenol, its pyrophosphate, monophosphate and fatty acid esters. The reactions of isopentenyl- and farnesyl pyrophosphates syntheses seemed to be rate-limiting steps.

The esterification of dolichol by rat liver microsomes

The incubation of 1-[3H)dolichols with cell-free preparations from various rat tissues resulted in the formation of a labeled material which possessed the characteristics of synthetic dolichol palmitate. Rat liver microsomes were found to be a good source of the acyltransferase activity, and the properties of the reaction were investigated using microsomal preparations. The reaction did not require ATP, CoA, or Mg2+ and was stimulated by the addition of phosphatidylcholine. The esterification of dolichol appears to be similar to the esterification of retinol. The fact that the esterification of dolichol is not depressed even in the presence of a several-fold excess of retinol is evidence that the two reactions are catalyzed by different enzymes.

Isolation of polyisoprenyl alcohols from Streptococcus faecalis

C(55)-isoprenyl alcohol and its derivatives have been isolated from Streptococcus faecalis and characterized. The relative amounts present as free alcohol, neutral lipid esters, and phosphate ester derivatives were determined. The chain lengths, mass spectra, and cis to trans ratio of double bonds are reported.

Dolichols, ubiquinones, geranylgeraniol and farnesol as the major metabolites of mevalonate in Phytophthora cactorum

Farnesol, geranylgeraniol, dolichols and ubiquinones were the main radioactive components of the unsaponifiable lipid recovered from Phytophthora cactorum grown in aerated cultures containing [2-(14)C]mevalonate. The (14)C recovered in each of these components was in the approximate proportion 2:4:3:5. When the culture was not aerated no radioactive ubiquinone was recovered. Most of the (14)C recovered in the dolichols was found in dolichol-15 (37%), with decreasing amounts in dolichol-14 (30%) and -13 (14%) and only a little (5%) in dolichol-16, whereas the major components, by weight, of the mixture (13mug/g of damp-dry tissue) were dolichol-14, -15 and -16 in the approximate proportion of 1:3:1. Radioautography of appropriate chromatograms indicated the presence also of traces of radioactivity in dolichol-9, -10, -11, -12 and -17. Most (80%) of the (14)C recovered in the ubiquinones was associated with ubiquinone-9, the rest being in ubiquinone-8. Most (80%) of the weight of ubiquinones (19mug/g of damp-dry tissue) was also ubiquinone-9. The identification of these compounds was by chromatographic methods and, for the ubiquinones and dolichols, was confirmed by mass spectrometry. In addition, the incorporation of 4R- and/or 4S-(3)H from [4-(3)H]-mevalonates showed the expected stereochemistry of biosynthesis, namely that farnesol, geranylgeraniol and ubiquinones were biogenetically all trans and the dolichols each contained three biogenetically trans isoprene residues, the remaining residues being biogenetically cis. The distribution of (14)C in the components of the whole lipid of the fungus was consistent with 97% of both the farnesol and geranylgeraniol being present as the fatty acid ester. The corresponding value for dolichols was 37%. The observation by other workers, that this fungus does not form either squalene or sterol, was confirmed.

Polyprenols of Aspergillus niger. Their characterization, biosynthesis and subcellular distribution

A polyprenol complex of Aspergillus niger was shown, by using spectrometric methods, to consist of a family of exo-methylene-hexahydroprenols that contain between 18 and 24 isoprene residues per molecule. Each prenol contains two trans residues, three saturated residues (alpha, omega and psi) and an exo-methylene substituent on the carbon atom beta to the isopropyl group in each omega-residue. The ubiquinone complex consisted of 90% ubiquinone-9, 9% ubiquinone-8 and 1% ubiquinone-10. The amount of polyprenol complex present reached a maximum of 1.7mg/culture bottle after 9-10 days of growth, coincident with the maximum weight of mycelium. The amount of ergosterol (10mg/culture bottle) and ubiquinone (1mg/culture bottle) reached a peak at 8 days. By the 13th day of growth the yield of ergosterol had fallen by 20% and that of ubiquinone by 85%. A study of the incorporation of [2-(14)C]mevalonate over different time-intervals confirmed that there was a slow turnover of prenol, a more rapid turnover of ergosterol and a very rapid turnover of ubiquinone. At any one time each member of the prenol complex had essentially the same specific radioactivity as other members of the complex. A similar conclusion was made about the ubiquinone mixture. Just over half of the polyprenol present was esterified to fatty acids. Subcellular fractionation studies indicated that the unesterified prenol is associated primarily with a mitochondrial fraction, whereas the ester is more widely distributed.