1 -Acylglycerol phosphate acyltransferase

The next step in phospholipid biosynthesis is catalyzed by 1-acylglycerol phosphate acyltransferase (the plsC gene product) which acylates the product of the PlsB step to form phosphatidic acid (Fig. 5). Phosphatidic acid comprises only about 0.1% of the total phospholipid in E. coli and turns over rapidly, a property consistent with its role as an intermediate in phospholipid synthesis. The 1-acylglycerol phosphate acyltransferase is thought to transfer unsaturated fatty acids selectively to the 2-position. The plsC gene is universally expressed in bacteria. 

A second esterification of this type leads to a phosphatidate (enzyme l-acylglycerol-3-phosphate acyltransferase 2.3.1.51). Unsaturated acyl residues, particularly oleic acid, are usually incorporated at C-2 of the glycerol. Phosphatidates (anions of phosphatidic acids) are the key molecules in the biosynthesis of fats, phospholipids, and glycolipids. 

Fig. 2. Acylglycerols. Biosynthesis of triacylglycer-ols in liver and adipose tissue cells. EC 1.1.1.8 Glycerol-3-phosphate dehydrogenase (NAD "). EC 2.3.1.15 (j ycerol-3-phosphate acyltransferase. EC 2.3.1.20 Diacylglycerol acyltransferase. EC 2.3.1.51 1-AcylgIycerol-3-phosphate acyltransferase. EC 3.1.3.4 Phosphatidate phosphatase. EC 6.2.1.3 Long-chaln-fatty acid-CoA ligase.

Hares, W. and Frentzen, M. (1991) Substrate specificities of the membrane-bound and partially purified microsomal acyl-CoA l-acylglycerol-3-phosphate acyltransferase from etiolated shoots of Pisum sativum (L.) Planta 185, 124-iM. 

Fig. 1. Functional expression of the cDNA from Limnanthes douglasii in E. coli JC201. Activities of 1-acylglycerol-3-phosphate acyltransferase were determined with either oleoyl-CoA (light bars) or erucoyl-CoA (dark bars) in membrane fractions of JC201 cells harbouring the vector pQE60 or the construct pQEL21, respectively, as described before [5].

In summary, we succeeded in the isolation of a cDNA from Limnanthes douglasii which encodes an erucoyl-CoA specific l-acylglycerol-3-phosphate acyltransferase. The deduced amino acid sequence shows substantial sequence similarity to the respective acyltransferase of E. coli. Consequently, the isolated cDNA is suitable for transforming rape-seed with the aim to increase the content of erucic acid in the fatty acid composition of rapeseed oil and, thus, to improve its industrial applicability. 

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