Chains isoprenoid-chained lipids

This chapter focuses on the use of different methods for isolation of alkylresorcinols. Alkylresorcinols are members of a lipid group called non-isoprenoid phenolic lipids. Different aspects of the extraction by classical methods and supercritical CO2 are discussed. Supercritical CO2 extraction of alkylresorcinols from rye bran is discussed for the first time. As compared to the classical extraction methods, supercritical CO2 gives higher yields and it allows the separation of the crude extrac into long- and short-chain alkylresorcinol homologues. 

For resorcinolic lipids, particularly those with long saturated side-chains, the use of polar solvents is important due to their amphiphilicity. The crude extracts in many cases are subjected to preliminary fractionation/purification either by solvent fractionation/partition or by application of chromatography. For prepurification of the material and its separation from polymerized phenolics, gel filtration on hydrophobic Sephadex or TSK gel is sometimes used. Silica gel is most frequently employed for the separation and/or purification of resorcinolic lipids, notably in some studies with Ononis species (12-14). The array of compounds reported appears partly attributable to methylation or acetylation reactions occurring during column chromatographic separation. An interesting approach for I the pre-purification and selective separation of resorcinolic lipid from phenolic lipids or resorcinolic lipids from impurities has recently been reported. A selective partitioning of different non-isoprenoid phenolic lipids... 

Molecular Dynamics Study of Isoprenoid-Chained Lipids Salient Features of Isoprenoid Chains As Compared with Ordinary Alkyl Chains... 

Synthetic isoprenoid-chained lipids are a new class of lipids, which have recently been attracted increasing attention [1-25). A salient feature of the isoprenoid-chained Hpids lies in their regularly branched chains consisting of poly-isoprenoid (C5) hydrophobic chains, which are remarkably different from those of ordinary lipids with linear hydrocarbon chains of variable length, different degree of unsaturation. 

I 9 Molecular Dynamics Study of Isoprenoid-Chained Lipids... 

Essentially the same consideration appUes to an inverted bicontinuous cubic phase (Qn) and an inverted hexagonal (Hn) phase, which are usually formed with lipids with long hydrophobic chains. Qn and Hn phases have recently received growing attention in the pharmaceutical or biological fields, for instance, as new carriers for drug-deUvery systems, and matrices for membrane protein crystallization [37-42]. The conventional (e.g., monoolein) Qn phase, however, often transforms into a soUd phase at low temperatures around 4°C [43-47], where temperature-sensitive proteins or actives are most preferably handled and preserved. It has recently been confirmed that isoprenoid-chained lipids can in fact give a range of Qn phases that are stable at low temperatures [13]. 

Rhodamine 6G long-chain hydrocarbons [169] squalene, a-amyrin [170] methyl esters of fatty acids [171] glycerides [91] sterols [172, 173] isoprenoids, quinones [HI] lipoproteins [174] glycosphingolipids [175] phenolic lipids [176] phosphonolipids [177] increasing the sensitivity after exposure to iodine vapor [178,179]... 

The hydrophobic components of many lipids consist of either isoprenoids or fatty acids and their derivatives 34 Isoprenoids have the unit structure of a five-carbon branched chain 34 Brain fatty acids are long-chain carboxylic acids that may contain one or more double bonds 34... 

Isoprene chains are sometimes used as lipid anchors to fix molecules to membranes (see p. 214). Chlorophyll has a phytyl residue (1 = 4) as a lipid anchor. Coenzymes with isoprenoid anchors of various lengths include ubiquinone (coenzyme Q 1 = 6-10), plastoqui-none (1 = 9), and menaquinone (vitamin K 1 = 4-6). Proteins can also be anchored to membranes by isoprenylation. 

Type V and Vi proteins carry lipid anchors. These are fatty acids (palmitic acid, myristic acid), isoprenoids (e.g., farnesol), or glycoli-pids such as glycosyl phosphatidylinositol (GPi) that are covalently bound to the peptide chain. 

To establish unambiguously the length of a hydrocarbon chain or the position of double bonds, mass spectral analysis of lipids or their volatile derivatives is invaluable. The chemical properties of similar lipids (for example, two fatty acids of similar length unsaturated at different positions, or two isoprenoids with different numbers of isoprene units) are very much alike, and their positions of elution from the various chromatographic procedures often do not distinguish between them. When the effluent from a chromatography column is sampled by mass spectrometry, however, the components of a lipid mixture can be simultaneously separated and identified by their unique pattern of fragmentation (Fig. 10-24). 

Some membrane proteins contain one or more covalently linked lipids of several types long-chain fatty acids, isoprenoids, sterols, or glycosylated derivatives of phosphatidylmositol, GPI (Fig. 11-14). The attached lipid provides a hydrophobic anchor that inserts into the lipid bilayer and holds the protein at the membrane surface. The strength of the hydrophobic interaction between a bilayer and a single hydrocarbon chain linked to a protein is barely enough to anchor the protein securely, but many proteins have more than one attached... 

In addition to NAD and flavoproteins, three other types of electron-carrying molecules function in the respiratory chain a hydrophobic quinone (ubiquinone) and two different types of iron-containing proteins (cytochromes and iron-sulfur proteins). Ubiquinone (also called coenzyme Q, or simply Q) is a lipid-soluble ben-zoquinone with a long isoprenoid side chain (Fig. 19-2). The closely related compounds plastoquinone (of plant chloroplasts) and menaquinone (of bacteria) play roles analogous to that of ubiquinone, carrying electrons in membrane-associated electron-transfer chains. Ubiquinone can accept one electron to become the semi-quinone radical ( QH) or two electrons to form ubiquinol (QH2) (Fig. 19-2) and, like flavoprotein carriers, it can act at the junction between a two-electron donor and a one-electron acceptor. Because ubiquinone is both small and hydrophobic, it is freely diffusible within the lipid bilayer of the inner mitochondrial membrane and can shuttle reducing equivalents between other, less mobile electron carriers in the membrane. And because it carries both electrons and protons, it plays a central role in coupling electron flow to proton movement. 

In addition to its role as an intermediate in cholesterol biosynthesis, isopentenyl pyrophosphate is the activated precursor of a huge array of biomolecules with diverse biological roles (Fig. 21-48). They include vitamins A, E, and K plant pigments such as carotene and the phytol chain of chlorophyll natural rubber many essential oils (such as the fragrant principles of lemon oil, eucalyptus, and musk) insect juvenile hormone, which controls metamorphosis dolichols, which serve as lipid-soluble carriers in complex polysaccharide synthesis and ubiquinone and plastoquinone, electron carriers in mitochondria and chloroplasts. Collectively, these molecules are called isoprenoids. More than... 

Many of the proteins of membranes are enzymes. For example, the entire electron transport system of mitochondria (Chapter 18) is embedded in membranes and a number of highly lipid-soluble enzymes have been isolated. Examples are phosphatidylseiine decarboxylase, which converts phosphatidylserine to phosphatidylethanolamine in biosynthesis of the latter, and isoprenoid alcohol phosphokinase, which participates in bacterial cell wall synthesis (Chapter 20). A number of ectoenzymes are present predominantly on the outsides of cell membranes.329 Enzymes such as phospholipases (Chapter 12), which are present on membrane surfaces, often are relatively inactive when removed from the lipid environment but are active in the presence of phospholipid bilay-ers.330 33 The distribution of lipid chain lengths as well as the cholesterol content of the membrane can affect enzymatic activities.332... 

The second major type of lipid found in some biological membranes is cholesterol. Cholesterol (fig. 17.5) is an isoprenoid compound with four fused rings, a short aliphatic chain, and a single hydroxyl group. It occurs in membranes both in its free form and esterified with long-chain fatty acids. Table 17.3 compares the lipid compositions of mem-... 

Coenzyme Q (ubiquinone) is an essential cofactor in the electron transport chain in which it accepts electrons from complex I and II. Coenzyme Q also serves as an important antioxidant in both mitochondria I and lipid membranes. Coenzyme Q is a lipid-soluble compound composed of a redox active quinoid moiety and a hydrophobic tail. The predominant form of coenzyme Q in humans is coenzyme Q10, which contains ten isoprenoid units in the tail, whereas the predominant form in rodents is coenzyme Q9, which has nine isoprenoid units in the tail. Coenzyme Q is soluble and mobile in the hydrophobic core of the phospholipid bilayer of the inner membrane of the mitochondria in which it transfers electrons one at a time to complex III of the electron transport chain. 

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