Isoprenoid hydrocarbons

Thus, the lipid biosynthetic enzyme system evolved in extreme halophiles to utilize the (halophilic) mevalonate pathway for synthesis of virtually all of its hydrocarbon (isoprenoid/isopranoid) chains, rather than the (non-halophilic) fatty-acid synthetase system which was retained only for synthesis of normal fatty acid chains required for incorporation into proteins of the red membrane (Pugh and Kates, unpublished data). Starting from acetate and involving lysine, which provides the branch-methyl and methine carbons [88]), the mevalonate pathway proceeds to geranylgeranyl-PP (GG-PP) [13,15,89] as follows ... 

Route B does not strictly represent a fractionation protocol but is worthy of highlighting in the instances where an alternative rapid procedure is preferred for the analysis of total FA. Here, an acid-catalyzed transesterification can be undertaken, converting total ester-finked acyl residues directly to their methyl esters. As a byproduct, nonsaponifiable lipids are also retained in this fraction (hydrocarbons, isoprenoids) and analyzed simultaneously by chromatographic techniques. While more rapid, the technique yields a more complex sample for analysis. 

Although the term terpene once referred only to hydrocarbons current usage includes functionally substituted derivatives as well grouped together under the general term isoprenoids Figure 26 6 (page 1086) presents the structural formulas for a number of representative examples The isoprene units m some of these are relatively easy to identify The three isoprene units m the sesquiterpene farnesol, for example are mdi cated as follows m color They are joined m a head to tail fashion... 

Fluorescein paraffin derivatives, waxes, hydrocarbons [140,141] aliphatic acids [142] hydroquinone and chlorinated derivatives [143] isoprenoids, quinones [111,144] oxathizine fungicides [145] barbiturates, phenothiazines [146]... 

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]... 

Some proteins can be posttranslationally modified by the addition of prenyl groups. Prenyl groups are long-chain, unsaturated hydrocarbons that are intermediates in isoprenoid synthesis. The farnesyl group has 15 carbons, and the geranylgeranyl has 20 carbons. They are attached to a cysteine residue near the end of the protein as a thiol ether (Protein-S-R). Other proteins can have a long-chain fatty acid (C14=myristoyl, C16=palmitoyl) attached to the amino terminus as an amide. These fatty acid modifications can increase the association of proteins with the membrane. 

Another relevant feature of the gas chromographic profile is the acyclic isoprenoid hydrocarbon pattern that is made evident with capillary columns or by the inclusion of the saturated fraction in 5 A (0.5 nm) molecular sieves or in urea. The predominant peaks usually correspond to the C19 (pristaine) and C20 (phytane) isomers, which ratios serve as an identification parameter [87], although the series extends to lower and higher homologues. 

Terpenes are a large and diverse class of compounds produced by a wide variety of organisms, though plants are an especially prolific source. The terms terpenoid and isoprenoid can be used interchangeably with terpene, though, strictly, terpenes are hydrocarbons (composed only of carbon and hydrogen) while terpenoids and iso-prenoids have been further functionalized. 

Porphyrins and Plant Pigments Chiorophyii Hemin Carotenes and Xanthophyiis > Chlorin Phaeophytin hydrocarbons Phytane, pristane, carotenoids, isoprenoids, alcohols, ketones, acids, porphyrins... 

The solubility of fuel oil no. 2, particularly the alkane and isoprenoid fractions, in seawater is increased by the presence of fulvic acid, although the solubilities of phenanthrene or anthracene, both polycyclic aromatic hydrocarbons, are unaffected by the presence of humic materials (Boehm and Quinn 1973). Unfiltered Narragansett Bay water was able to dissolve 1,560 g/L of fuel oil no. 2, although removal of... 

Orphan skeletons are emphasized in boldfece characters. Found both in the Tertiary and the Triassic eras, they have no equivalent in extant organisms and cannot be accounted for by di enetic transformations alone. They comprise xanthenoxanthene quinones, quincyte pigments of likely polyketide origin (Prowse 1991), and three series of isoprenoids polycyclic hydrocarbons from the... 

Significant amounts of larger hydrocarbons are also generated by plants and emitted to the atmosphere. The larger hydrocarbon compounds generally fall under the classification of isoprenoids, or terpenoids, con-... 

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... 

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