Isoprenoid Chain Research Articles

Antioxidant action of ubiquinol homologues with different isoprenoid chain length in biomembranes

Ubiquinones (CoQn) are intrinsic lipid components of many membranes. Besides their role in electron-transfer reactions they may act as free radical scavengers, yet their antioxidant function has received relatively little study. The efficiency of ubiquinols of varying isoprenoid chain length (from Q 0 to Q 10) in preventing (Fe 2+ + ascorbate)-dependent or (Fe 2+ + NADPH)-dependent lipid peroxidation was investigated in rat liver microsomes and brain synaptosomes and mitochondria. Ubiquinols, the reduced forms of CoQ n , possess much greater antioxidant activity than the oxidized ubiquinone forms. In homogenous solution the radical scavenging activity of ubiquinol homologues does not depend on the length of their isoprenoid chain. However in membranes ubiquinols with short isoprenoid chains (Q 1–Q 4) are much more potent inhibitors of lipid peroxidation than the longer chain homologues (Q 5–Q 10). It is found that: i) the inhibitory action, that is, antioxidant efficiency of short-chain ubiquinols decreases in order Q 1 > Q 2 > Q 3 > Q 4; ii) the antioxidant efficiency of long-chain ubiquinols is only slightly dependent on their concentrations in the order Q 5 > Q 6 > Q 7 > Q 8 > Q 9 > Q 10 and iii) the antioxidant efficiency of Q 0 is markedly less than that of other homologues. Interaction of ubiquinols with oxygen radicals was followed by their effects on luminol-activated chemiluminescence. Ubiquinols Q 1–Q 4 at 0.1 mM completely inhibit the luminol-activated NADPH-dependent chemiluminescent response of microsomes, while homologues Q 6–Q 10 exert no effect. In contrast to ubiquinol Q 10 (ubiquinone Q 10) ubiquinone Q 1 synergistically enhances NADPH-dependent regeneration of endogenous vitamin E in microsomes thus providing for higher antioxidant protection against lipid peroxidation. The differences in the antioxidant potency of ubiquinols in membranes are suggested to result from differences in partitioning into membranes, intramembrane mobility and non-uniform distribution of ubiquinols resulting in differing efficiency of interaction with oxygen and lipid radicals as well as different efficiency of ubiquinols in regeneration of endogenous vitamin E.

Analysis of the organic matter in five oil shales

The organic matter in five oil shales (three Kimmeridge clays, one Oxford clay and one from the Julia Creek deposits in Australia) was concentrated by acid demineralisation and then further degraded, first by reduction with LiAlH 4 then by oxidation with perTFA and/or KMnO 4. At each stage, products were separated into soluble and insoluble fractions by solvent extraction. The fractions were analysed using a range of appropriate techniques, including solution and solid state 1H and 13C n.m.r., FT-i.r., g.p.c. and g.c.-m.s.. These analyses confirmed previous observations that oil shales, like coals, consist of a mobile and a rigid phase. In addition, it was found that a close relation existed between chemical structures present in the bitumens and in their associated kerogens, and that one of the kerogens differed from the other four in that isoprenoid chains predominated over straight chains throughout the system. Oxidation with perTFA gave residues that were predominantly aliphatic in character. PerTFA appeared to be a better oxidant than KMnO 4 for structural analysis in that it gave fewer secondary products.

Fully saturated menaqionones in the archaebacteriumPyrobaculum islandicum

The anaerobic, thermophilic archaebacterium, Pyrobaculum islandicum (Geo 3) was examined for the presence of lipoquinones. Thin layer chromatographic, HPLC, UV, and mass spectroscopic analysis showed that a menaquinone was present. No evidence was found for substitution of the 2-methyl-3-polyisoprenyl-1,4-naphthoquinone ring nucleus. However, the C3 isoprenoid chain consisted of six fully saturated units, and shows that the major menaquinone in this organism corresponds to 2-methyl-3-VI,V,IV,III,II,I-dodecahydrohexaprenyl-1, 4-naphthoquinone (MK-6H12).

Action of a homologous series of ubiquinols on lipid peroxidation in brain mitochondrial and synaptosomal membranes

The effects of inhibition of ubiquinols and ubiquinones with various length of isoprenoid chain on the lipid peroxidation in membranes of brain mitochondria and synaptosomes were studied. The efficiency of inhibition effects of ubiquinols depends on the length of isoprenoid chain. Ubiquinols with shorter isoprenoid chains demonstrated more effective inhibition.

Analog pigment studies of chromophore-protein interactions in metarhodopsins

Several analogue pigments have been prepared containing retinals altered at the cyclohexyl ring or proximal to the aldehyde group in order to examine the role of the chromophore in the formation of the metarhodopsin I and II states of visual pigments. Deletion of the 13-methyl group on the isoprenoid chain did not affect metarhodopsin formation. However, analogue pigments containing chromophores with modified rings did not show the typical absorption changes associated with the metarhodopsin transitions of native or regenerated rhodopsins. In particular, 4-hydroxyretinal pigments did not show clear transitions between the metarhodopsin I and metarhodopsin II states. Pigment formed with an acyclic retinal showed no evidence by absorption spectroscopy of metarhodopsin formation. A retinal altered by substitution of a five-membered ring containing a nitroxide required a more acidic pH than the native pigment for formation of the metarhodopsin II state. ESR data suggest that the ring remains buried within the protein through the metarhodopsin II state. However, the Schiff base linkage is susceptible to hydrolysis of hydroxylamine in the metarhodopsin II state. These data indicate that (1), in the transition from rhodopsin to metarhodopsin II, major protein conformational changes are occurring near the lysine-retinal linkage whereas the ring portion of the chromophore remains deeply buried within the protein and (2) pigment absorptions characteristic of the metarhodopsin I and II states may be due to specific protein-chromophore interactions near the region of the chromophore ring.

Occurrence of a resistant biopolymer in the L race of Botryococcus braunii

A resistant biopolymer, PRB L, occurs in the outer walls of the L race of Botryococcus braunii. It accounts for a larger fraction of the total biomass than PRB A and B do in the A and B races. The PRB L structure is mainly based on long (up to C 30 saturated, isoprenoid hydrocarbon chains probably linked by ether bridges. Most of these isoprenoid chains exhibit regular head-to-tail linkages. Therefore, PRB L does not belong to the same family as PRB A and B, the structures of which are based on long, normal hydrocarbon chains. The only hydrocarbon produced by the L race algae is a lycopadiene so a relationship between hydrocarbon and PRB structure can be considered in this L race as has already been demonstrated for the A race.

Glutaraldehyde Derivatives as Building Blocks for Stereoselective (Z)-C5Elongation of a Regular Isoprenoid Chain

L'ethylenedioxy-5,5 pentanal et sa t-butylimine peuvent servir de «synthons» non isoprenoide polyvalent pour la construction d'un chaine terpenoide cisoide via une aldolisation croisee controlee

Isoshowacene, A C 31 hydrocarbon from Botryococcus braunii var. showa

-Two C 31 acyclic hydrocarbons, showacene and isoshowacene, were obtained from a 16-day-old air-lift culture of Botryococcus braunii var. showa. The compounds were isolated as a 17:10 mixture by reversed-phase HPLC. Upon analysis by GC-MS and by 1H and 13C NMR, the compounds were found to be 1′–3 fused triterpenes of the botryococcene type bearing a single additional methyl at opposite ends of the isoprenoid chains.

Preliminary analysis of Monterey kerogen by mild stepwise oxidation with sodium dichromate in glacial acetic acid

Kerogen from Monterey shale was degraded by a controlled, mild stepwise oxidation with sodium dichromate in acetic acid. The products of each step were examined by capillary gas chromatography and combined gas chromatography-mass spectrometry analyses of their methyl esters. Major oxidation products were saturated normal monocarboxylic acids (C 6-C 34), saturated normal α,ω-dicarboxylic acids (C 4-C 34), and isoprenoid acids (C 14-C 21, except C 18). Less dominant were aromatic acids, branched monocarboxylic acids (C 6-C 16), cyclic structures, heterocyclic compounds, as well as some unidentified compounds. On the basis of the evidence obtained from the qualitative and quantitative variation of the products with duration of oxidation, the following results were obtained: 1. (a) the kerogen nucleus is mainly composed of long-chain polymethylene, cross-linked aliphatic structure from which protrude n- alkyl chains and minor amounts of isoprenoid and non-isoprenoid branched hydrocarbons; 2. (b) the periphery, compared to the nucleus, contains a greater proportion of n- alkyl and isoprenoid moieties, particularly the C 14, C 16, and C 18 n- alkyl chains as well as the C 15 and C 16 isoprenoid chains; 3. (c) other subordinate structures present include phenyl and tolyl groups as well as alicyclic and heterocyclic compounds.

Polarographic properties of ubiquinones with isoprenoid chains of different lengths

It has been shown that in aqueous ethanolic solutions the polarographic potentials E1/2 for ubiquinones with isoprenoid chains with different lengths are the same, −0.235 V (relative to a normal calomel electrode) at pH 7.9, and correspond to quasi-irreversible reduction with the addition of 2e−/2H+. It has been found that the potential E1/2 for the ubiquinone UQ-O having no isoprenoid chain is more positive by 57 mV relative to the potentials of the other ubiquinones.

Membrane-stabilizing effect of vitamin E: Effect of α-tocopherol and its model compounds on fluidity of lecithin liposomes

The effects of vitamin E (α-tocopherol) and its model compounds on the fluidity of liposomes composed of dipalmitoylphosphatidylcholin (DPPC) and fatty acids were investigated by the measurement of the fluorescent polarization (P) using 1,6-diphenyl-1,3,5-hexatriene (DPH) as a plobe. Although all tocopherols decreased the fluidity of liposomes which was perturbed by the inclusion of an unsaturated fatty acid having more than one double bond, α-tocopherol was more effective than the others. The fluidity in arachidonic acid-containing liposomes was decreased most in the presence of α-tocopherol and was decreased considerably by the inclusion of model compounds having a side chain at least one isoprene unit or a long straight chain instead of isoprenoid side chain. However the chromanol with methyl group instead of the above side chain, and phytol, having no chromanol moiety, had no effect. These results show that a structural requirement for a membrane stabilization is to be either the chromanol moiety with methyl groups born on its aromatic ring or a side chain of appropriate length; an isoprenoid side chain of full length or one containing 4′a- and 8′a-methyl groups is not necessarily needed.

Interaction of vitamin E and its model compounds with unsaturated fatty acids in homogeneous solution.

Either alpha-tocopherol (vitamin E) or one of its model compounds having side chains of different length at the 2-position of alpha-tocopherol, forms complexes with an unsaturated fatty acid in methanol. For complex formation, the isoprenoid side chain and hydroxy group of alpha-tocopherol are unessential and, rather, the methyl groups attached to the aromatic ring of the chromanol moiety seems to be responsible. For better interaction, more than three methylene-interrupted Z double bonds of a fatty acid are necessary. These findings are incompatible with the hypothesis of Diplock and Lucy on the interaction of vitamin E with each polyunsaturated fatty acid.

Quenching of the intrinsic tryptophan fluorescence of mitochondrial ubiquinol--cytochrome-c reductase by the binding of ubiquinone.

1. The quenching by ubiquinone (Q) of the intrinsic fluorescence of tryptophan residues within ubiquinol--cytochrome-c reductase (complex III) has been exploited to provide direct information on the interaction between these two components of the mitochondrial respiratory chain. 2. The fluorescence quenching data have been corrected for inner filter effects and interpreted using the classical Stern-Volmer and modified Stern-Volmer plots. The latter of these plots allows computation of both the dissociation constant (Kd) of complex formation between ubiquinone and complex III, and the percentage of fluorophores accessible to quenching. 3. It is found that different Q homologues bind to complex III with different affinities depending upon the length of the isoprenoid chain: 2,3-dimethoxy-5-methyl-6-decyl-1,4-benzoquinone, an analogue of Q2, exhibits the same Kd as Q2. Furthermore, the accessibility of fluorophores to quenching was lower for Q1 than for the other quinones tested. 4. The binding affinity of Q2 to complex III depends upon the redox state of the enzyme. 5. Addition of the complex III inhibitor, antimycin, has very little effect on the binding affinity or on the accessibility of fluorophores to the quencher. 6. Addition of the inhibitor myxothiazol has a similar effect to reducing complex III with ascorbate. 7. Reconstitution of complex III into asolectin lipid vesicles gives similar qualitative results to the enzyme in solution regarding both the redox state and the addition of inhibitors.

Isoprenoid biosynthesis in multiple sclerosis, II. A possible role of NADPH.

Genetic predisposition in MS, influence of fat consumption on the disease, and excretion of lipid metabolites in urine led us to investigate isoprenoid metabolism in this disease. Ubiquinone concentration and biosynthesis was normal in lymphocytes. Cytochrome oxidase, which contains an isoprenoid side chain, was normal in activity. Cholesterol biosynthesis from acetate was found to be elevated in MS, and so was triglyceride biosynthesis. Increased biosynthesis may offer a very simple explanation to all the metabolites excreted (3-methylglutaconic acid, 2-hydroxy-2-methyl-3-butenoic acid and adipic acid). Increased biosynthesis may be caused by an elevated NADPH/NADP ratio, since such an elevation may also account for many other biochemical anomalies in MS. Elevated NADPH/NADP ratio may be of direct importance in the pathogenesis.

13C NMR assignments of the isoprenoid chain carbons of retinoids from empirical chemical shift differences

Abstract13C NMR assignments have been made for a series of 36 α‐ and 3,4‐dehydroretinoids with different substituents (alcohol, ester, aldehyde and acid) and for their separated E and Z geometrical isomers. The assignments were made by using 2D heteronuclear‐correlated NMR experiments. From the chemical shift data of 24 systematically related retinoids, empirical chemical shift changes due to four polar end groups (alcohol, aldehyde, carboxylic acids and esters), three chain configurations (all‐E, 9Z and 13Z), and two ring substitutions (2,6,6‐trimethyl‐cyclohex‐2‐enyl and 2,6,6‐trimethylcyclohexa‐1,3‐dienyl) were determined. All trends were found to be independent of each other, except for the dependence of the chemical shift change of the 13Z‐isomers on the polar end groups. The chemical shift changes were used to predict the chemical shifts of other retinoids based on two different ring structures (2,6,6‐trimethylcyclohexenyl and 4‐methoxy‐2,3,6‐trimethylphenyl).

Membrane stabilization of vitamin E; interactions of α-tocopherol with phospholipids in bilayer liposomes

13C Spin-lattice relaxation times (T 1) of 13C-labeled α-cocopherol in three kinds of liposomes varying in their contents of arachidoyl residues have been measured by 13C-NMR spectroscopy. On the basis of T 1 values, it is proved that the segmental motion of isoprenoid side chain of α-tocopherol tends to increase with an increase in the distance from the chromanol moiety, and that three methyl groups attached on the aromatic ring, have some affinity to ansaturated fatty acid residues rather than those of the isoprenoid side chain. These results are incompatible with the hypothesis of Diplock et al. (1) which 4′a- and 8′a-methyl groups of isoprenoid side chain are fitted in the Z-pockets of arachidoyl chain of polyunsaturated lipids in membrane.

The effect of ring substituents on the mechanism of interaction of exogenous quinones with the mitochondrial respiratory chain

In uncoupled pig-heart mitochondria the rate of the reduction of duroquinone by succinate in the presence of cyanide is inhibited by about 50% by antimycin. This inhibition approaches completion when myxothiazol is also added or British anti-Lewisite-treated (BAL-treated) mitochondria are used. If mitochondria are replaced by isolated succinate:cytochrome c oxidoreductase, the inhibition by antimycin alone is complete. The reduction of a plastoquinone homologue with an isoprenoid side chain (plastoquinone-2) is strongly inhibited by antimycin with either mitochondria or succinate:cytochrome c reductase. The reduction by succinate of plastoquinone analogues with an n-alkyl side chain in the presence of mitochondria is inhibited neither by antimycin nor by myxothiazol, but is sensitive to the combined use of these two inhibitors. On the other hand, the reduction of the ubiquinone homologues Q 2, Q 4, Q 6 and Q 10 and an analogue, 2,3-dimethoxyl-5- n-decyl-6-methyl-1,4-benzoquinone, is not sensitive to any inhibitor of QH 2:cytochrome c reductase tested or their combined use, either in normal or BAL-treated mitochondria or in isolated succinate:cytochrome c reductase. It is concluded that quinones with a ubiquinone ring can be reduced directly by succinate:Q reductase, whereas those with a plastoquinone ring can not. Reduction of the latter compounds requires participation of either center i or center o (Mitchell, P. (1975) FEBS Lett. 56, 1–6) or both, of QH 2:cytochrome c oxidoreductase. It is proposed that a saturated side chain promotes, while an isoprenoid side chain prevents reduction of these compounds at center o.

Determination of the critical micelle concentration of short-chain ubiquinones in model systems

We have investigated the critical micelle concentrations of short-chain ubiquinone and ubiquinol homologs in water, aqueous buffers and ethanol-water mixtures. The physical state of ubiquinones becomes nonmonomeric at definite concentration that can be identified because the aggregation is accompanied by a red shift of λ max and a decrease of the extinction coefficient. Systematic studies following the transition dipole moment against quinone concentration have established that the critical micelle concentration is a function of isoprenoid chain length and state of oxidation of the quinones and of the dielectric constant and ionic strength of the medium. The thermodynamics of micelle formation point out that the quinone ring has a strong tendency to be located in a hydrophobic environment.

The senescence retarding ability and metabolism of trihydroxy-zeatin in Avena leaf segments

6-(2,3,4-Trihydroxy-3-methylbutylamino) purine, trivial name trihydroxy-zeatin (THZ), an oxidation product of zeatin was applied via the epidermis or cut end of Avena leaf segments. THZ did not retard senescence of the segments in either case. With epidermal application THZ remained unmetabolised while the cut end method of application resulted in its metabolism to more polar THZ metabolites of unknown identity. The Avena leaf tissue did not apparently cleave the isoprenoid side chain of the THZ molecule.

The structure of an inhibitor of cholesterol biosynthesis isolated from barley.

Purification of the oily, nonpolar fraction of high protein barley (Hordeum vulgare L.) flour by high pressure liquid chromatography yielded 10 major components, two (I, II) of which were potent inhibitors of cholesterogenesis in vivo and in vitro. The addition of purified inhibitor I (2.5-20 ppm) to chick diets significantly decreased hepatic cholesterogenesis and serum total and low density lipoprotein cholesterol and concomitantly increased lipogenic activity. The high resolution mass spectrometric analysis and measurement of different peaks of inhibitor I gave a molecular ion at m/e 424 (C29H44O2) and main peaks at m/e 205, 203, and 165 corresponding to C13H17O2, C13H15O2, and C10H13O2 moieties, respectively. which are characteristic of d-alpha-tocotrienol. This identification was confirmed against synthetic samples. The tocotrienols are widely distributed in the plant kingdom and differ from tocopherols (vitamin E) only in three double bonds in the isoprenoid chain which appear to be essential for the inhibition of cholesterogenesis.