Lysophosphatidate acyltransferase

Cao, Y.-Z., Oo, K.-C., Huang, A.H.C. (1990) Lysophosphatidate acyltransferase in microsomes from maturing seeds of meadowfoam Limnanthes alba). Plant Physiol. 94, 1199-1206. 

Oo, K.-C. and Huang, A.H.C. (1989) Lysophosphatidate acyltransferase activities in the microsomes from palm endosperm, maize scutellum, and rapeseed cotyledon of maturing seeds. Plant Physiol. 91, 1288-1295. 

Laurent P, Huang AHC. Organ- and development-specific acyl coenzym A lysophosphatidate acyltransferases in palm and meadowfoam. Plant Physiol 1992 99. 1711-1715. 

Esterification of glycerol 3-phosphate with a long-chain fatty acid produces a strongly amphipathic lysophosphatidate (enzyme glycerol-3-phosphate acyltransferase 2.3.1.15). In this reaction, an acyl residue is transferred from the activated precursor acyl-CoA to the hydroxy group at C-1. 

Fig. 2. Targeted lipidomics of 2-AG metabolism. Postulated pathways for 2-AG metabolism. Abbreviations PLC, phospholipase C DAG, diacylglycerol DGL, diacylglycerol lipase MGL, monoacylglycerol lipase PLA, phospholipase A AT, acyltransferase TAGL, triacylglycerol lipase PIP2, phosphatidylinositol bisphosphate ABHD-6/12 hydrolase lyso-PL, lysophospholipid lyso-PA, lysophosphatidic acid PA, phosphatidic add P, phosphatase COX, cydooxygen-ase LOX, lipoxygenase CYP450, cytochrome P450 CDP, cytidine diphosphate.

AG can be converted back into complex lipid molecules by anabolic enzymes. This recycling process is mediated by MAG kinases (MAGK) and acyltransferases (AT) to generate 2-arachidonoyl-lysophosphatidic acid and DAG, respectively. In turn, these lipids can be then converted into glyceropho-spholipids or TAG (Fig. 2). 

Fig. 10. Coordinate regulation of fatty acid and phospholipid metabolism. The pleiotropic regulator ppGpp regulates transfer of fatty acids to the membrane via inhibition of the PlsB acyltransferase step, coordinating phospholipid synthesis with macromolecular synttesis. PlsB inhibition leads to the accumulation of long-chain acyl-ACPs that feedback inhibit their own synthesis at the point of initiation (inhibition of acetyl-CoA carboxylase and FabH) and elongation, by inhibition of Fabl. LPA, lysophosphatidic acid G3P, glycerol-3-phosphate.

Since phosphatidic acid serves as a precursor of phospholipids, galactolipids, and TGs, it is not surprising that its own synthesis has been reported in four plant compartments plastids, ER, mitochondria, and Golgi bodies. In each case, esterification of the first acyl group to the in-1 position of glycerol-3-phosphate is catalyzed by glycerol-3-phosphate acyltransferase. Lysophosphatidic acid acyltransferase then completes the synthesis by acylating the sn-2 position. However, plastidial and extraplastidial acyltransferases show distinct differences in structure and specificity. Analysis of these differences and the different compositions of plastid and non-plastid membranes led to the prokaryotic/ eukaryotic two-pathway scheme for plant lipid synthesis shown in Fig. 3. 

In the plastids, acyltransferases provide a direct route for entrance of acyl groups from ACP to membrane lipids. Since this is the standard pathway for phosphatidic acid synthesis in E. coli and cyanobacteria, both the enzymes of phosphatidic acid synthesis in plastids and the glycerolipid backbones they produce are termed prokaryotic . In both chloroplasts and non-green plastids, the glycerol-3-phosphate acyltransferase is a soluble enzyme that, unlike the E. coli enzyme, shows preference for 18 1-ACP over 16 0-ACP. The lysophosphatidic acid acyltransferase, which is a component of the inner envelope of plastids, is extremely selective for 16 0-ACP. The presence of a 16-carbon fatty acid at the... 

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.

Key Words Acyltransferase diacylglycerol glycerol-3-phosphate Kennedy pathway Land s cycle lysophosphatidic acid triacylglycerol. 

Knutzon, D.S., Hayes, T.R., Wyrick, A., Xiong, H., Davies, H.M., and Voelker, T.A. Lysophosphatidic acid acyltransferase from coconut endosperm mediates the insertion of laurate at the sn-2 position of triacylglycerols in lauric rapeseed oil and can increase total laurate levels. Plant Physiology 120, 739-746, 1999. 

Oil Indian mustard [11] Introduction of very long chain fatty adds by introduction of enzymes (fatty add desaturases and elongases, lysophosphatidic add acyltransferase) involved with their biosynthesis... 

After consumption of usual food fats, the major products of digestion that are absorbed are 2 in-MG and FFA. In the small intestinal cells, the sn-2-MG react with activated FFA to be converted by a multienzyme complex into TG. The excess FFA react with sn-3-glycerophosphate to form lysophospha-tidic acids, which are further converted into phosphatidic acids. Dephosphorylation results in ot-1, 2-DG, which are precursors of both TG and PL. What happens after the influx of sn-l,3-DG or sn-l(3)-MG into the intestinal cell is less clear. A series of competing reactions must be considered, such as complete digestion, acylation, transacylation, phosphorylation, and intact excretion out of the intestinal cells as well. Lipases are present in the intestinal cells but their action seems to be reduced by other intestinal cell constituents (28). The sn-1,2-DG seem to be poor substrates for intestinal TG synthesis (29), whereas in-l-MG can be phosphorylated into lysophosphatidic acid (30) and possibly be metabolized fur-dier as described above. It has to be realized, however, that j -3-glycerophosphate acyltransferase possesses fatty acid selectively, incorporating mainly palmitic acid at the sn-1... 

LPAAT - acyltransferase of lysophosphatidic acid GPAT - glycerol-3-phosphate acyltransferase DGAT - diacylglycerol acyltransferase PPA - phosphatase of phosphatidic acid. 

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