Phosphatidic acid functional derivatives

The first experiments implicating a role for PLD activity in neutrophil function were performed by Cockcroft and colleagues (Cockcroft Stutchfield, 1989 Cockcroft, 1992) who measured phosphatidic acid accumulation in cells whose membrane phospholipids or ATP were radiolabelled. These experiments showed that phosphatidic acid accumulation during cell activation did not derive from DAG, but rather was directly generated from a phospholipid. Phosphatidic acid production from DAG (generated by PLC)... 

The simplest of the glycerophospholipids is phosphatidic acid, in which phosphate is linked to the third hydroxyl function, forming a phosphate ester. More complex glycerophospholipids are derivatives of phosphatidic acid in which one of several groups is attached commonly choline, ethanolamine, serine, or myo-inositol. Structures are collected in table 19.1. 

The 1, 2-diglyceride arises by a dephosphorylation of a diacyl-phospha-tidic acid (a glycerophosphatide without the base) in the presence of a specific phosphatase. The phosphatidic acids which are intermediates in the biosynthesis of lecithins are the result of a combination, in the presence of ATP and a specific enzyme, of a-glycerophosphoric acid with two molecules of fatty add activated by CoA. These compounds of aliphatic acids and CoA are provided by the fatty acid cycle functioning in the direction of biosynthesis. The enzyme catalysing acyl transfer has a special spedfidty for the acyl-CoA derivatives of the Cu and Cjg acids. 

In higher plants, the lipolytic enzymes and their physiological functions are not well characterized [1]. iMost reports demonstrated that phospholipid catabolism in plants is achieved by the concerted actions of membrane-bound enzymes including phospholipase D, phosphatidate phosphatase, lipolytic acyl hydrolases and lipoxygenases [1,2]. With the exception of the phospholipase D, the literature on plant phospholipases is still very limited. We previously reported that tonoplast from Acer pseudoplatanus cells contains small amounts of phosphatidic acid and lysophospholipids, which were produced together with free fatty acids, particularly after addition of Ca " [31. These data suggested the possible involvement of phospholipase D and phospholipase A in the metabolism of vacuolar membrane lipids. The phospholipase activities were studied by following the hydrolysis of added sn-2-[14c]linoleyl-PC to tonoplast vesicles. Tonoplast was obtained by osmotic lysis of pure preparations of vacuoles isolated from protoplasts derived from Acer pseudoplatanus cells [4]. This present work demonstrated clearly the presence of phospholipase D and phospholipase Ai activities associated with the tonoplast of Acer, The phospholipase Ai showed an optimal activity at pH about 6-6.5, did not necessarily require divalent cations, but was stimulated by Mg- and particularly by Ca. This work presents the first evidence for the presence of phospholipases A in plant cells. 

Pettitt, T. R., Martin, A., Horton, T., Liossis, C., Lord, J. M., and Wakelam, M. J. O. (1997). Diacylglycerol and phosphatidate generated by phospholipases C and D respectively have distinct fatty acid compositions and functions Phospholipase D-derived diacylglycerol does not activate protein kinase C in PAE cells. J. BioL Chem. 272, 17354-17359. 

---