Triacylglycerol diacylglycerol acyltransferase

FIGURE 25.20 Triacylglycerols are formed primarily by the action of acyltransferases on mono- and diacylglycerol. Acyltransferase in E. coli is an integral membrane protein (83 kD) and can utilize either fatty acyl-CoAs or acylated acyl carrier proteins as substrates. It shows a particular preference for palmitoyl groups. Eukaryotic acyltransferases nse only fatty acyl-CoA molecnles as substrates. 

S Cases, S J Smith, Y-W Zheng, HM Myers, SR Lear, E Sande, S Novak, C Collins, CB Welch, AJ Lusis, SK Erickson, RV Farese Jr. Identification of a gene encoding an acyl CoA diacylglycerol acyltransferase, a key enzyme in triacylglycerol synthesis. Proc Natl Acad Sci (USA) 95 13018-13023, 1998. 

Dahlqvist, A., Stahl, U., Lenman, M., Banas, A., Lee, M., Sandager, L., Ronne, H., and Stymne, S. 2000. Phospholipid diacylglycerol acyltransferase An enzyme that catalyzes the acyl-CoA-independent formation of triacylglycerol In yeast and plants. Proc. Natl. Acad. Sci., 97, 6487-6492. 

Fig. 5. Pathway depicting how flux through phosphatidylcholine (product of reaction 3) can promote acyl group diversity in plant triacylglycerols. Production of 18 2 (boxed) at the sn-2 position and its transfer to TG is used as a sample modification. Other fatty acid alterations may be substituted. Enzymes 1, glycerol-3-phosphate acyl-CoA acyltransferase and lysophosphatidic acid acyl-CoA acyltransferase 2, phosphatidic acid phosphatase 3, diacylglyceroliCDP-aminoalcohol aminoalcoholphosphotransferase 4, 18 l-desaturase or other fatty acid modifying enzyme 5, phosphlipid diacylglycerol acyltransferase 6, diacylglycerol acyltransferase 7, acyl-CoA phosphatidylcholine acyltransferase or phospholipase plus acyl-CoA synthetase.

Lung, S.C. R.J. Weselake. Diacylglycerol acyltransferase a key mediator of plant triacylglycerol synthesis. Lipids 2QQ6, 41, 1073-1088. 

Ichihara, K., T. Takahashi, and S. Fujii. 1988. Diacylglycerol acyltransferase in maturing safflower seeds its influences on the fatty acid composition of triacyglycerol and on the rate of triacylglycerol synthesis. Biochim. Biophys. Acta 958 125-129. 

Saha, S., B. Enugutti, S. Rajakumari, and R. Rajasekharan. 2006. Cytosolic triacylglycerol biosynthetic pathway in oilseeds. Molecular cloning and expression of peanut cytosolic diacylglycerol acyltransferase. Plant Physiol. 141 1533-1543. 

Key Words Diacylglycerol acyltransferase epoxygenase industrial oil resins triacylglycerol vernoleate. 

Owen, M.R., Corstorphine, C.C. Zammit, V.A. (1997) Biochem. J., 323, 17-21. Overt and latent activities of diacylglycerol acyltransferase in rat liver microsomes possible roles in very-low-density lipoprotein triacylglycerol secretion. 

Rustan, A.C., Nossen, J.O, Christiansen, E.N. Drevon, C.A. 1988. J. LipidRes. 29 1417-1426. Eicosapentaenoic acid reduces hepatic synthesis and secretion of triacylglycerol by decreasing the activity of acyl-coenzyme A 1,2-diacylglycerol acyltransferase. 

Synthesis of triacylglycerols requires the enzyme diacylglycerol acyltransferase (EC 2.3.1.20). The enzyme is particulate and has been studied in many mammalian tissues (O Doherty, 1978). In some cases activity is stimulated by the additon of phosphatidylcholine (O Doherty et al, 1974) and there is also evidence that the Z protein may be involved in stimulating acyltransferase activity (O Doherty and Kuksis, 1975). 1,2-Isomers of diacylglycerol are about twice as effective as 2,3-isomers. The enzymes show little chain-length specificity, however (e.g. Hill etal, 1968). 

Chemicals known to inhibit phosphatidic acid phosphatase (25 mM EDTA) and diacylglycerol acyltransferase (5 mM DIPFP, 1.5 mM 2-BrOA) decreased the rate of incorporation of C-erucoyl-CoA into triacylglycerols by 85%, 60% and 84%, respectively, but this inhibition was not accompanied by an accumulation of C-erucoyl moieties in LPA, PA or DAG, or in other polar lipids [108]. 

The enzymes for phosphatidate synthesis, acyl CoA synthetase, glycerol 3-phosphate acyltransferase and monoacylglycerol acyltransferase, are on both the outer mitochondrial membrane and the endoplasmic reticulum membrane. Diacylglycerol acyltransferase is only on the endoplasmic reticulum it may use either diacylglycerol phosphate synthesized on the endoplasmic reticulum or that synthesized on the mitochondrion. Triacylglycerol synthesized on the endoplasmic reticulum membrane may then enter lipid droplets either in the cytosol or, in the liver and intestinal mucosa, the lumen of the endoplasmic reticulum for assembly into lipoproteins - chylomicrons in the intestinal mucosa (section 4.3.2.2) and very low-density lipoprotein in the liver (section 5.6.2). 

ROLE OF CHOLINEPHOSPHOTRANSFERASE AND DIACYLGLYCEROL ACYLTRANSFERASE IN CHANNELING UNUSUAL FATTY ACIDS INTO THE TRIACYLGLYCEROL POOL DURING OILSEED DEVELOPMENT... 

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