Presence Of Dolichol Research Articles

The effect of dolichol on the structure and phase behaviour of phospholipid model membranes

The effect of dolichol C(95) on the structure and thermotropic phase behaviour of dipalmitoylphosphatidylcholine, dipalmitoylphosphatidylethanolamine and stearoyloleoylphosphatidylethanolamine has been examined by synchrotron X-ray diffraction and differential scanning calorimetry. The presence of dolichol C(95) had no detectable effects on the temperature of either the gel to ripple or the ripple to liquid-crystal phase transition of dipalmitoylphosphatidylcholine. A proportionate increase of a few degrees in the temperature of the gel to lamellar liquid-crystal phase transition is observed in dispersions of dipalmitoylphosphatidylethanolamine and significantly there is a decrease in the temperature of the lamellar to non-lamellar phase transition of stearoyloleoylphosphatidylethanolamine. There was no significant change in the bilayer repeat spacing of all three mixed dispersions in gel phase in the presence of up to 20 mol% dolichol C(95). Electron density calculations showed that there was no change of bilayer thickness of dipalmitoylphosphatidylcholine with incorporation of up to 7.5 mol% dolichol C(95). These data suggest that effect of dolichol on the phospholipid model membranes depend on both the head group and the hydrocarbon chains of the phospholipid molecules. The presence of dolichol in phosphatidylcholine bilayers conforms to a model in which the polyisoprene compound is phase separated into a central domain sandwiched between the two monolayers in gel phase. In bilayers of phosphatidylethanolamines dolichol tends to stabilize the bilayers in gel phase at low temperatures and destabilize the bilayers in lamellar disordered structure at high temperatures. Non-lamellar structures coexist with lamellar disordered phase over a wide temperature range suggesting that dolichol is enriched in domains of non-lamellar structure and depleted from lamellar phase. These findings are useful to understand the function of dolichol in cell membranes.

1H-NMR and 13C-NMR lipid profiles of human renal tissues.

Lipids from human renal tissues are studied by means of (1)H- and (13)C-NMR spectroscopy. The total lipid fractions obtained from healthy kidneys, malignant renal cell carcinomas, and benign oncocytomas are characterized and analyzed to elucidate the main differences between the functional and neoplastic tissues. In all cases the lipid components are well identified. The healthy kidney is characterized by high amounts of triglycerides and the presence of cholesterol in its free form. On the contrary, renal cell carcinomas contain high amounts of cholesterol that are almost completely esterified as oleate, suggesting an intracellular localization of the cholesteryl esters synthesis. Cholesteryl esters are considered markers of renal cell carcinomas, thus supporting recent theories that these compounds play a leading role in cell proliferation. Oncocytomas are particularly rich in phosphatidylcholine and, analogous to the healthy kidney, are completely lacking in cholesteryl esters. Healthy kidneys and oncocytomas appear to have other similarities if compared with renal cell carcinomas: a very high fatty acyl/cholesterol ratio, the presence of dolichols, and a higher grade of unsaturation. The (13)C data suggest a new method for the direct evaluation of the saturated/unsaturated fatty acyl ratio.

Characterization of the isoprenoid chain of coenzyme Q in Plasmodium falciparum

Little is known about isoprenoid biosynthesis in parasitic protozoa. The presence of dolichol and isoprenylated proteins has been detected in Plasmodium falciparum, but no studies are available about the biosynthesis of the isoprenic side chain attached to the benzoquinone ring of coenzyme Q. In the present study, using metabolic labelling with different intermediates, we demonstrated the presence of an active isoprenoid pathway for the biosynthesis of the isoprenic chain of coenzyme Q. Our results show that P. falciparum is able to synthesize different homologs (coenzyme Q 8 and coenzyme Q 9), depending on the given intermediate. Parasites treated with nerolidol at doses 2.2 times below the IC 50 showed a decreased ability to synthesize the isoprenic chain attached to coenzyme Q at all intraerythrocytic stages. Treatment with nerolidol arrested development of the intraerythrocytic stages of the parasites, indicating that the drug may have an antimalarial potential.

Characterization of the isoprenoid chain of coenzyme Q in Plasmodium falciparum.

Little is known about isoprenoid biosynthesis in parasitic protozoa. The presence of dolichol and isoprenylated proteins has been detected in Plasmodium falciparum, but no studies are available about the biosynthesis of the isoprenic side chain attached to the benzoquinone ring of coenzyme Q. In the present study, using metabolic labelling with different intermediates, we demonstrated the presence of an active isoprenoid pathway for the biosynthesis of the isoprenic chain of coenzyme Q. Our results show that P. falciparum is able to synthesize different homologs (coenzyme Q(8) and coenzyme Q(9)), depending on the given intermediate. Parasites treated with nerolidol at doses 2.2 times below the IC(50) showed a decreased ability to synthesize the isoprenic chain attached to coenzyme Q at all intraerythrocytic stages. Treatment with nerolidol arrested development of the intraerythrocytic stages of the parasites, indicating that the drug may have an antimalarial potential.

Degenerative Disorders of the Central Nervous System

Degenerative Disorders of the Central Nervous System

Presence of dolichol and its derivatives in human blood.

Optimal conditions for the quantitative estimation of dolichol in human plasma were determined. Because of the large amounts of other lipids present in the blood, the extraction procedure, the procedure for hydrolysis, and the HPLC procedure are of decisive importance. Human plasma contains dolichol, dolichyl esters, and dolichyl phosphate at concentrations of 41, 102, and 55 ng/g, respectively. These polyisoprenoid lipids are associated with the high density lipoprotein fraction. The relative amounts and compositions of dolichyl esters in the plasma are similar to those observed in isolated human liver microsomes and Golgi vesicles. Sixty percent of the fatty acids present are saturated and almost no long-chain polyunsaturated components are present. There is no correlation between blood dolichol content and weight, sex, dietary state, or plasma cholesterol level, but there is an inverse relationship to plasma triglyceride content. A linear increase in the total plasma dolichol content with increasing age was found. In a few pathological conditions where the level of blood cholesterol was increased, the total blood dolichol content was not affected. Apparently, dolichol is a stable lipid component of human high density lipoprotein.

Effects of dolichol on membrane permeability

Small vesicles containing the tetra-anionic fluorescent probe calcein were prepared by sonication of mixtures of plant phosphatidylethanolamine, plant phosphatidylcholine, and dolichol. Following chromatography, the isolated vesicles were found to retain entrapped calcein over the temperature range of 15 to 40°C. Utilizing an assay measuring the fluorescence quenching of entrapped calcein by cobalt ions, the presence of dolichol in the membranes was found to promote the permeability of the phospholipid bilayers to the divalent cation. The permeability was shown to be dependent on temperature with an increase in rate of 17-fold between 15 and 35°C although the plant phospholipids used in these experiments have no known phase transition within this temperature range. The incorporated dolichol was distributed uniformly throughout the vesicle population. Similar vesicles prepared from phosphatidylethanolamine and phosphatidylcholine without added dolichol, from phosphatidylcholine alone, or with phosphatidylcholine and dolichol were far less permeable to the divalent cation under the same assay conditions. These results demonstrate that dolichols have significant effects on the permeability properties of phospholipid bilayers that contain phosphatidylethanolamine.

The presence of dolichol in liver supernatant.

The presence of dolichol in liver supernatant.

Inhibition of polyisoprenoid and glycoprotein biosynthesis causes abnormal embryonic development.

Compactin, a potent inhibitor of polyisoprenoid biosynthesis, induces abnormal gastrulation during sea urchin development at concentrations that have no effect on earlier embryonic development or on macromolecular synthesis. Three lines of evidence suggest that the developmental lesion caused by compactin results from inhibition of dolichol biosynthesis and a concomitant inhibition in the biosynthesis of the oligosaccharide chains of N-linked glycoproteins. (i) Embryos cultured in the presence of compactin gastrulate normally when supplemented with dolichol alone, whereas supplementation with cholesterol or coenzyme Q or both does not prevent the compactin-induced developmental lesion. (ii) Exogenously supplemented [3H]dolichol is incorporated into a compound with the chromatographic properties of oligosaccharide-pyrophosphoryldolichol. (iii) Embryos cultured in the presence of compactin exhibit a decreased capacity to synthesize mannose-labeled glycolipids and N-linked glycoproteins. This decrease in synthesis is abolished if the embryos are cultured in the presence of dolichol along with compactin.

The presence of dolichol in a lipid diphosphate N-acetylglucosamine from Saccharomyces cerevisiae (baker's yeast)

The lipid moiety of a lipid diphosphate N-acetylglucosamine, an intermediate in glycosylation of proteins, was studied. Ozonolysis of the compound gave evidence for an alpha-saturated isoprene unit. Alkaline hydrolysis of the glycolipid, followed by high-pressure liquid chromatography, showed the presence of a series of polyprenol homologues identical with those isolated directly from Saccharomyces cerevisiae (baker's yeast). No particular homologue was preferred in the enzymic transfer of N-acetylglucosamine 1-phosphate to endogenous dolichol monophosphate.