Glycerol metabolic pathways

The fatty acids released on triacylglycerol hydrolysis are transported to mitochondria and degraded to acetyl CoA, while the glycerol is carried to the liver for further metabolism. In the liver, glycerol is first phosphorylated by reaction with ATP. Oxidation by NAD+ then yields dihydroxyacetone phosphate (DHAP), which enters the carbohydrate metabolic pathway. We ll discuss this carbohydrate pathway in more detail in Section 29.5. 

LPA, i.e. monoacyl-glycerol-3-phosphate, can be formed and degraded by multiple metabolic pathways (Fig. 1). Depending on the precursor molecule and respective pathway, the fatty acid chain in LPA differs in length, degree of saturation and position (sn-1 or sn-2), which has an influence on biological activity. LPA... 

Figure 5-4. Metabolic activities of major organs in the fed state. The relative activities of major metabolic pathways or processes in each of the organs are indicated by their font sizes. The exchange of nutrient materials and fuel molecules through the bloodstream illustrates the interrelationships of these organs. In the absorptive condition, all organs share the bounty of nutrients made available by digestion of food by the intestine. PPP, pentose phosphate pathway FA, fatty acids TAG, triacyl-glycerol.

Cjthanqj Cjcetat ( utyra C Butanoj Cj -Butanedi Fig.1. Metabolic pathways of glycerol metabolism... 

As already mentioned, early attempts have been focused on the enzymatic production of lecithin in lecithin liposomes (Schmidli et al, 1991). The metabolic pathway was the so-called Salvage pathway, which converts glycerol-3-phosphate to phosphatidic acid, then diacylglycerol and hnally phosphatidylcholine. Production of the cell boundary from within corresponds to autopoiesis and would close the circle between minimal cell and the autopoietic view of cellular life. 

Synthesis of most phospholipids starts from glycerol-3-phosphate, which is formed in one step from the central metabolic pathways, and acyl-CoA, which arises in one step from activation of a fatty acid. In two acylation steps the key compound phosphatidic acid is formed. This can be converted to many other lipid compounds as well as CDP-diacylglycerol, which is a key branchpoint intermediate that can be converted to other lipids. Distinct routes to phosphatidylethanolamine and phosphatidylcholine are found in prokaryotes and eukaryotes. The pathway found in eukaryotes starts with transport across the plasma membrane of ethanolamine and/or choline. The modified derivatives of these compounds are directly condensed with diacylglycerol to form the corresponding membrane lipids. Modification of the head-groups or tail-groups on preformed lipids is a common reaction. For example, the ethanolamine of the head-group in phosphatidylethanolamine can be replaced in one step by serine or modified in 3 steps to choline. 

Active compounds were retested in medium containing glycerol as a carbon source. Glycerol does not require PFK for introduction into bacterial energy metabolism pathways. Compounds that were as toxic to the recombinant bacteria in the presence of glycerol as they were in mannitol could not be acting via inhibition of PFK. Conversely, compounds that are significantly more toxic in... 

Fatty acids are incorporated into complex lipids through de novo synthetic and remodeling pathways. As detailed below and shown in Fig. 2a, intracellular pools of acyl-CoA are involved in processes outside of lipid metabolism and, in many instances, function as important regulatory molecules. Figure 2b illustrates an overview of glycerol phospholipid synthesis and how fatty acids in the form of acyl-CoA enter these metabolic pathways. Readers are referred to the article entitled Lipid Synthesis in this series for specific details regarding these pathways. 

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.

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