ubiquinone and pentane

Microsomes and mitochondria prepared from rat liver were extracted with n-pentane, a procedure which does not denature enzyme proteins. Protein and phospholipid were not extracted, but 75-80% of the total dolichol, 80-100% of the ubiquinone and 85-95% of the cholesterol were removed from both organelles by this procedure. Enzymatic and non-enzymatic lipid peroxidation in microsomes and non-enzymatic peroxidation in mitochondria were strongly inhibited when ubiquinol was reinserted into n-pentane-extracted membranes. When reconstitution with dolichol was performed, lipid peroxidation was increased or unchanged, while cholesterol decreased this activity in a concentration-dependent manner. In reconstitution experiments ubiquinol and dolichol together were less inhibitory than ubiquinol alone, whereas cholesterol accentuated the inhibitory effect of ubiquinol. Reconstitution with dolichols of different lengths, dolichyl esters or with alpha-unsaturated polyprenols further demonstrated that dolichol is not an antioxidant. It appears that mevalonate pathway lipids influence lipid peroxidation in membranes by modifying the properties of the bilayer.

Topics: Animals; Cholesterol; Dolichols; Enzyme Activation; In Vitro Techniques; Intracellular Membranes; Lipid Peroxidation; Male; Microsomes, Liver; Mitochondria, Liver; Pentanes; Rats; Rats, Sprague-Dawley; Ubiquinone

The role of ubiquinone in the Golgi apparatus is still unknown, even if it might be considered as a lipid marker of the Golgi compartment because of its high content in these subcellular fractions. In vivo modulation of ubiquinone with ethanol and in vitro pentane extraction show that ubiquinone is not required either for NADH-ferricyanide reductase, acetaldehyde dehydrogenase activity, or Ca2+ and Mg2+ stimulated ATPases. Since ubiquinone does not seem to be involved in these enzymic activities in Golgi compartments, other possible functions are discussed, related to a role in membrane fluidity or as a barrier to the propagation of free radicals.

Topics: Aldehyde Oxidoreductases; Animals; Ca(2+) Mg(2+)-ATPase; Calcium-Transporting ATPases; Cell Fractionation; Ethanol; Female; Golgi Apparatus; Liver; NADH, NADPH Oxidoreductases; Pentanes; Phosphotransferases; Rats; Rats, Inbred Strains; Subcellular Fractions; Transferases (Other Substituted Phosphate Groups); Ubiquinone

Extraction of endogenous ubiquinone from lyophilized beef heart mitochondria results in increases of both the order parameter of the spin label 5-NS and of the rotational correlation time of 16-NS; reconstitution with the pentane extract results in restoration of the original spectral parameters. On the other hand, addition of purified ubiquinone homologs restores the original spectra only in the case of 16-NS, whereas the order parameter of 5-NS is restored by addition of mixed phospholipids. The same amounts of ubiquinone homologs incorporated in mixed phospholipid vesicles induce much lower effects. It is suggested that ubiquinone in mitochondria is intercalated with the lipid chains of the membrane in such a way to perturb the fluidity of the hydrophobic core.

Topics: Animals; Cattle; Cyclic N-Oxides; Electron Spin Resonance Spectroscopy; Intracellular Membranes; Membrane Fluidity; Membrane Lipids; Mitochondria, Heart; Pentanes; Spin Labels; Ubiquinone

The membrane-bound NADH oxidase of Paracoccus halodenitrificans was inhibited by dicoumarol, 2-n-heptyl-4-hydroxy-quinoline-N-oxide (HQNO), and exposure to ultraviolet light (at 366 nm). When the membranes were extracted with n-pentane, NADH oxidase activity was lost. Partial restoration was achieved by adding the ubiquinone fraction extracted from the membranes. Succinate oxidation was not inhibited by dicoumarol or HQNO, but was affected by ultraviolet irradiation or n-pentane extraction. However, the addition of the ubiquinone fraction to the membranes extracted with n-pentane did not restore enzyme activity. These observations suggested that NADH and succinate were not oxidized through a common ubiquinone pool.

Topics: Dicumarol; Electron Transport; Enzyme Inhibitors; Hydroxyquinolines; Multienzyme Complexes; NADH, NADPH Oxidoreductases; Oxidoreductases; Oxygen Consumption; Paracoccus; Pentanes; Quinones; Ubiquinone; Ultraviolet Rays