Glycerol phosphate moiety

Lipoteichoic acid is a component of the Gram-positive bacterial cell surface. The typical chemical structure of Staphylococcus aureus LTA is shown in Fig. 8 [109,110,111], which is composed of a glycolipid moiety and a hydrophilic poly(glycerol phosphate) moiety. The former moiety shows bacterial species-specific structural variation. The glycerol units in the later moiety are partially substituted with (oligo)-D-alanyl ( 70%) and/or (oligo)-lV-acetyl-o -D-glucosaminyl ( 15%) residues. 

Fig. 9. Phospholipid turnover. The 1,2-diacylglyceroI kinase cycle involves the (1) transfer of the sn-1 -glycerol phosphate moiety from phosphatidylglycerol to MDO by the enzyme MdoB. (2) Diacylglycerol kinase converts the diacylglycerol to phosphatidic acid, which can regenerate the phosphatidylglycerol (see Fig. 6). Phosphatidylethanolamine cycling involves (3) the transfer of an acyl chain to membrane lipoprotein and (4) re-esterification of the 1-position by 2-acylgiycerophosphoethanolamine (Aas).

The synthesis of this polymer in a cell-free system has been achieved, and it was found that UDP-2-acetamido-2-deoxy-D-glu-copyranose donates the entire 2-acetamido-2-deoxy-D-glucopyranosyl phosphate moiety intact, and that CDP-D-glycerol donates the glycerol phosphate moiety. The presence of lipid intermediates in this system has been reported. ... 

Enzymes that degrade phospholipids are called phospholipases. They are classified according to the bond cleaved in a phospholipid (fig. 19.11). Phospholipases Al and A2 selec- tively remove fatty acids from the sn-1 and sn-2 positions, i respectively. Phospholipase C cleaves between glycerol and the phosphate moieties phospholipase D hydrolyzes the [ head-group moiety X from the phospholipid. Lysophospho- lipids, which lack a fatty acid at the sn-1 or sn-2 position, j are degraded by lysophospholipases. f Phospholipases are found in all types of cells and in... 

Figure 6. Biosynthetic pathways for PAF. PAF can be synthesized by two different metabolic pathways. The first pathway (I) is initiated by phospholipase A2 hydrolysis of alkyl-acyl-GPC, followed by acetylation of lyso-PAF. The second pathway (II) acetylates 1-O-alkyl-2- yso-sn-g Ycero-3-phosphate, followed by dephosphorylation to yield 1-0-alkyl-2-acetyl-s/7-glycerol. This moiety subsequently condenses with CDP-choline to produce PAF.

The proposed catalytic mechanism involves a proton relay-type reaction where an immobilized HjO molecule serves as the nucleophile, a role normally filled by serine. The proton relay system is buried in the hydrophobic active-site wall. Ca " " binds the phosphate moiety of the substrate and, serving as a Lewis acid, polarizes the ester bond at the carbonyl oxygen. The HjO molecule, immobilized by the Asp-His pair attacks the carbonyl of the substrate and donates an H" " to His. The alkoxy oxygen of the glycerol backbone then retrieves the H" " from the His to complete the reaction. 

Fatty acids released from the acyl carrier protein moiety of FAS can be activated in the cytosol and esterified to alpha glycerol phosphate to form phosphatidic acid. Phosphatidic acid can then proceed in two major directions. 

Phosphatidylcholine can be completely hydrolysed with aqueous acid to produce fatty acids, glycerol, phosphoric acid and choline. With alkali, the fatty esters are preferentially hydrolysed, leaving the glycero-phosphoryl-cholines, which can in turn hydrolyse slowly into glycerophosphoric acid and choline. Enzymatic hydrolysis occurs selectively at different ester sites by several phospholipases to produce a range of products. Phospholipases A1 and A2 are obtained commercially from snake venom. They hydrolyse the fatty acid at the -1 and sn-2 positions respectively, to produce lysophosphatidyl-choline. Phospholipase C catalyses the hydrolysis of the phosphate moiety to give 1,2-diacylglycerols and phosphorylcholine. Phospholipase D found in plant tissues mainly catalyses hydrolysis of the phosphate ester to produce choline and phosphatidic acids (1). 

A lipoteichoic acid with a lipid anchor which is a galactofuranosyl-P-1,3-glycerol with different fatty acid residues esterified to the two adjacent OH groups in the glycerol moiety and a non-glycosylated, linear, unbranched glycerol phosphate chain. The hydrophilic backbone consists of only 10 glycerophosphate units esterified with D-alanine to the extent of 30%. Isol. from Streptococcus sp. DSM 8747. Shows antitumour activity. 

Indole-3-glycerol phosphate is the penultimate substrate which is fed into the tryptophan synthase complex. This enzyme is composed of two subunits (as an a2 and 2-tetramer) which utilizes substrate channeling to complete the construction of this amino acid. The a-subunit catalyzes the formation of indole from indole-3-glycerol phosphate and the -subunit catalyzes the condensation of indole to a serine-derived aminoacrylate moiety bound to pyridoxal monophosphate (PLP). 

An early observation by the Hokins, and one which has subsequently been confirmed several times, was that renewal of the inositol and phosphate moieties of the PI molecule was more rapid during stimulation, but there was not an equivalent increase in the incorporation of glycerol into PI (see 2). The obvious conclusion from this is that a cycle of reactions occurs in which PI is both broken down and resynthesized, but that the glycerol backbone of the molecule is conserved throughout this process. There is still some dispute over the exact nature of this cycle of reactions, which will be discussed later. 

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