Acyl- glycerol-3-phosphate

Lecithins and related phospholipids usually contain a saturated fatty acid in the C-l position but an unsaturated acid, which may contain from one to four double bonds, at C-2. Arachidonic acid is often present here. Hydrolysis of the ester linkage at C-2 yields a l-acyl-3-phosphoglycerol, better known as a Iysophosphatidylcholine. The name comes from the powerful detergent action of these substances which leads to lysis of cells. Some snake venoms contain phospholipases that form Iysophosphatidylcholine. Lysophosphatidic acid (l-acyl-glycerol-3-phosphate) is both an intermediate in phospholipid biosynthesis (Chapter 21) and also a signaling molecule released into the bloodstream by activated platelets.15... 

CTP phosphocholine cytidylyltransferase (3) glycerol kinase (4) acyl-CoA glycerol-3-phosphate acyltransferase (5) acyl-CoA acyl glycerol-3-phosphate acyltransferase (6) phosphatidic acid phosphatase (7) CDP-choline diacylglycerol phosphocholine transferase. 

Altered lauric acid distribution in TG 1 -acyl-glycerol-3-phosphate acyltransferase Coconut Rapeseed... 

Figure 3.3 Enzyme systems associated with glycerolipid formation, (a) Glycerol kinase (EC 2.7.1.30) (b) glycerol-3-phosphate acyltransferase (EC 2.3.1.15) (GPAT) (c) 1-acyl-glycerol-3-phosphate acyltransferase (EC 2.3.1.51) (LPAAT) (d) phosphatidate phosphatase (EC 3.1.3.4) (e) diacylglycerol acyltransferase (EC 2.3.1.20) (DAGAT) (f) cholinephosphotransferase (EC 2.7.8.2) (CPT) (g) 1-acylglycerophosphocholine acyltransferase (EC 2.3.1.23).

The activities of glycerol-3-phosphate acyltransferase and 1-acyl-glycerol-3-phosphate acyItransferase, the enzymes involved in the first steps of glycerolipid synthesis, have been characterized in crude extracts of Andbaena variabilis (Lem and Stumpf, 1984b Stapleton and Jaworski, 1984a,b). These enzymes use acyl-carrier protein (AGP), but not coenzyme... 

Acylation describes the process by which a fatty acid reacts with another molecule (e.g. glycerol phosphate) or with a protein, to facilitate attachment of the protein to a membrane. 

Synthesis of a molecule of TAG from glycerol phosphate and fatly acyl CoA This pathway involves four reactions, shown in Figure 16.14. These include the sequential addition of two fatty acids from fatty acyl CoA, the removal of phosphate, and the addition of the third fatty acid. 

PA is the precursor of many other phosphoglycerides. The steps in its synthesis from glycerol phosphate and two fatty acyl CoAs were illustrated in Figure 16.14, p. 187, in which PA is shown as a precursor of triacylglycerol. [Note Essentially all cells except mature ery-. throcytes can synthesize phospholipids, whereas triacylglycerol synthesis occurs essentially only in liver, adipose tissue, lactating mammary glands, and intestinal mucosal cells.]... 

Figure 18-5 A current concept of the electron transport chain of mitochondria. Complexes I, III, and IV pass electrons from NADH or NADPH to 02, one NADH or two electrons reducing one O to HzO. This electron transport is coupled to the transfer of about 12 H+ from the mitochondrial matrix to the intermembrane space. These protons flow back into the matrix through ATP synthase (V), four H+ driving the synthesis of one ATP. Succinate, fatty acyl-CoA molecules, and other substrates are oxidized via complex II and similar complexes that reduce ubiquinone Q, the reduced form QH2 carrying electrons to complex III. In some tissues of some organisms, glycerol phosphate is dehydrogenated by a complex that is accessible from the intermembrane space.

Fatty acyl-CoA is the donor of the fatty acyl group to the two nonphosphorylated positions of glycerol phosphate to make a phos-phatidic acid. 

Fatty acyl- Glycerol Step 1 Phosphatidic CoA + 3-phosphate acid... 

These acylations are catalyzed by glycerol phosphate acyltransferase. In most phosphatidates, the fatty acyl chain attached to the C-1 atom is saturated, whereas the one attached to the C-2 atom is unsaturated. 

Two other enzymes that we will encounter later, glycerol phosphate drogenase (p. 528) and fatty acyl CoA dehydrogenase (p. 624), likewise transfer their high-potential electrons from FAD Hi to Q to form ubiquinol (QH f), the reduced state of ubiquinone. These enzymes oxidize glycerol and fats, respectively, providing electrons for oxidative phosphorylation, These enzymes also do not pump protons. 

Fig. 3. Major biosynthetic pathways and enzymes for the endocannabinoid 2-arachidonoyl-glycerol (2-AG). DAG, di-acyl-glycerol lipase PA, phosphatidic acid PI, phosphoinositide PLC, phospholipase C. P represents a phosphate group...

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. 

Fig. 5. Transfer of fatty acyl groups to the membrane. Panel A, PlsX catalyzes the transfer of the fatty acid from acyl-ACP to phosphate to form the activated acylphosphate. PlsY acylates the 1-position of the glycerol backbone using acylphosphate as the acyl donor. Panel B, a fatty acid is transferred from acyl-ACP or acyl-CoA to the 1-position of sn-glycerol-3-phosphate (G3P) by glycerol phosphate acyltransferase (PlsB). A second fatty acid is transferred to the 2-position by the 1-acylgIycerol phosphate acyltransferase (PlsC). PlsC is common to both pathways.

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).

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