Prenol lipids

Prenol Lipid derived from 5-carbon isoprene units. 

Other lipid compounds include prenol lipids, saccharolipids, sphingolipids and polyketides (Figure 6.5). Each of these has a slightly different structure, but they have the same indicative properties of the other compounds in the lipid class. 

This does not mean that dried-droplet preparations cannot be imaged. Indeed, clearly dependent on the chemical structure, certain compounds do remain in the tissue (e.g., the (prenol) lipid ion at 610.444). For specific analyte molecules such as these latter compounds, the dried-droplet method can thus be used as a specific sample preparation method to wash away unwanted compounds. In this respect, it is interesting to note that the corpora cardiaca are the main synthesis sites of the insect juvenile hormone (JH), also a prenol lipid of the class of terpenoids. JH as such is not secreted in the adult stage of the insect imaged here, but the presence of other terpenoids in this tissue is expected. 

Prenol lipids (PRs) are synthesized from the 5-carbon precursors iso-pentenyl diphosphate and dimethylallyl diphosphate. The simple iso-prenoids (linear alcohols, diphosphates, etc.) are formed by the successive addition of C5 imits and are classified according to the number of these terpene imits. This class includes the carotenoids, which are precursors of vitamin A and also possess antioxidant effects. Prenol lipids containing more than 40 carbon atoms are termed polyterpenes. 

The outer surfaces of bacteria are rich in specialized polysaccharides. These are often synthesized while attached to lipid membrane anchors as indicated in a general way in Eq. 20-20.136/296a One of the specific biosynthetic cycles (Fig. 20-9) that depends upon undeca-prenol phosphate is the formation of the peptidoglycan (murein) layer (Fig. 8-29) of both gram-negative and gram-positive bacterial cell walls. Synthesis begins with attachment of L-alanine to the OH of the lactyl... 

More recently, a third omics field, lipidomics, was developed. Lipidomics was developed to attempt to provide a system in which to quantitatively profile all of the lipid molecules in a given species or in a tissue within that species (Han, 2011 Welti, 2011). Not surprisingly, a new nomenclature system has been developed to help to define and catalog the various lipids in the lipidome of each species. In this system, tocopherols and tocotrienols are part of the category called prenols (Table 11.1). Currently, the main database for lipidomics information in the USA is the LIPID-MAPS (2011) and its Prenol category contains the four known tocopherols (oc, (3, y, 5), four known tocotrienols (a, [3, y, 5), and a total of 1177 Prenols. Each of the eight individual tocopherols and tocotrienols are sometimes referred to as vitamers. 

The range of donor substrates that are tolerated by these enzymes has also been explored. A series of analogs was prepared, each one differing from 10 only in the identity of the lipid chain, and the set was screened for biological activity [56]. It was discovered that conjugates of C50 and C55 prenols were substrates, while those compoimds with shorter ([Pg.142]

The most recent definition of lipids was provided by a group of lipid chemists who formed the consortium of lipid metabolites and pathways strategy (Lipid MAPS). They defined lipids based on the origin of the lipid structures as hydrophobic or amphipathic small molecules that may originate entirely or, in part, by carbanion-based condensations of thioesters (fatty acids, polyketides, etc.) and/or by carbocation-based condensations of isoprene units (prenols, sterols, etc.). In this book, this definition, its classification (see the following), and its recommended nomenclature are largely accepted. 

The dolichol moiety of lipid-intermediates is not homogeneous but a mixture of 14-20 isoprene units [71-73]. For the yeast OST it was shown that the enzyme hardly discriminates specific isoprene chain lengths [74]. Whether unsaturated poly-prenols, preferred in eubacterial cell wall synthesis, will be accepted is not known. However, the formation of the DolPP-GlcNAc, i.e. the first step in lipid-linked precursor formation shows an absolute dependency for saturation of the a-isoprenoid unit, i.e for dolichol-type polyprenols [74], what seems to be generally true for other eukaryotic glycosyltransferases involved in lipid-linked sugar formation [75, 76]. 

---