Lysophospholipases

Sometimes called lysophospholipase to distinguish it from other esterases of this kind... 

Two possible pathways for the biosynthesis of 2-AG have been proposed (1) a phospholipase C (PLC) hydrolysis of membrane phospholipids followed by a second hydrolysis of the resulting 1,2-diacylglycerol by diacylglycerol lipase or (2) a phospholipase Ai (PLA,) activity that generates a lysophospholipid, which in turn is hydrolyzed to 2-AG by lysophospholipase C (Fig. 5) (Piomelli, 1998). Alternative pathways may also exist from either triacylglycerols by a neutral lipase activity or lysophosphatidic acid by a dephosphorylase. The fact that PLC and diacylglycerol lipase inhibitors inhibit 2-AG formation in cortical neurons supports the contention that 2-AG is, at least predominantly, biosynthesized by the PLC pathway (Stella, 1997). However, a mixed pathway may also be plausible. 

Fifth, esterase activity can be due to enzymes with nonesterase main activities. Thus, lysophospholipase (EC 3.1.1.5) and carbonic anhydrase (EC... 

The weak base chloroquine (30-300 pM, 30 minutes, either in the presence or absence of serum) increases the endosomal pH (83) within a few minutes (45), leading to pH values close to 6.3 in both endosomes and lysosomes and therefore preventing lysosomal degradation. As a mechanism of action, a direct inhibition of lysosomal hydrolases (cathepsin B1 and some phospholipases and lysophospholipases) is reported (82). In Kupffer cells, effects are tolerated at concentrations of 40 pM or less for up to four hours and are irreversible within two hours after medium replacement (82). 

This enzyme, known officially as lysophospholipase [EC 3.1.1.5] as well as by other common names lecithinase B, lysolecithinase, and phospholipase B, catalyzes the hydrolysis of 2-lysophosphatidylcholine to yield glycero-phosphocholine and a fatty acid. See Micelle... 

Selected entries from Methods in Enzymology [vol, page(s)] Glycosylphosphatidylinositol-specific phospholipase D, 197, 567 solubilization and purification of rat tissue phospholipase D, 197, 575 lysophospholipase D, 197, 583. 

MONOACYLGLYCERIDE LIPASE 1-Acyl-sn-glycerol 3-phosphate, LYSOPHOSPHOLIPASE D ACYLGLYCERON E-PHOSPHATE REDUCTASE... 

Acyl-sn-glycero-3-phosphoethanolamine, LYSOPHOSPHOLIPASE D Acyl halide reduction to alcohols (or aldehydes),... 

LYSOPHOSPHOLIPASE D N-Alkylimino ester reduction, BOROHYDRIDE REDUCTION... 

LYSOPHOSPHOLIPASE 2-Lysophosphatidylcholine, LYSOPHOSPHOLIPASE LYSOPHOSPHOLIPASE LYSOPHOSPHOLIPASE D Lysopine,... 

Most cells continually degrade and replace their membrane lipids. For each hydrolyzable bond in a glycerophospholipid, there is a specific hydrolytic enzyme in the lysosome (Fig. 10-15). Phospholipases of the A type remove one of the two fatty acids, producing a lysophospholipid. (These esterases do not attack the ether link of plasmalogens.) Lysophospholipases remove the remaining fatty acid. 

FIGURE 10-15 The specificities of phospholipases. Phospholipases Ai and A2 hydrolyze the ester bonds of intact glycerophospholipids at C-l and C-2 of glycerol, respectively. Phospholipases C and D each split one of the phosphodiester bonds in the head group. Some phospholipases act on only one type of glycerophospholipid, such as phosphatidylinositol 4,5-bisphosphate (shown here) or phosphatidylcholine others are less specific. When one of the fatty acids has been removed by a type A phospholipase, the second fatty acid is cleaved from the molecule by a lysophospholipase (not shown). 

In the duodenum, dietary lipids are degraded by pancreatic enzymes triacylglycerol by pancreatic lipase, phospholipids by phospholipase A2 and lysophospholipase, and cholesteryl esters by cholesterol esterase. Enzyme release from the pancreas is controlled by cholecystokinin, produced by cells in the intestinal mucosa. 

Enzymes that degrade phospholipids are called phospholipases. They are classified according to the bond cleaved in a phospholipid (fig. 19.11). Phospholipases Al and A2 selec- tively remove fatty acids from the sn-1 and sn-2 positions, i respectively. Phospholipase C cleaves between glycerol and the phosphate moieties phospholipase D hydrolyzes the [ head-group moiety X from the phospholipid. Lysophospho- lipids, which lack a fatty acid at the sn-1 or sn-2 position, j are degraded by lysophospholipases. f Phospholipases are found in all types of cells and in... 

Carboxylesterase Arylesterase Triacylglycerol lipase Phospholipase A2 Lysophospholipase Acetylesterase Acetylcholinesterase Cholinesterase... 

Wang, A., et al. 1999. A specific human lysophospholipase cDNA cloning, tissue distribution and kinetic characterization. Biochim Biophys Acta 1437 157. 

Gassama-Diagne, A., Fauvel, J., and Chap, H. (1989) Purification of anew, calcium-independent, high molecular weight phospholipase A2/lysophospholipase (phospholipase B) from guinea pig intestinal brush-border membrane, J. Biol. Chem. 264, 9470-9475. 

Quistad, G.B., Barlow, C., Winrow, C.J., Sparks, S.E., Casida, J.E. (2003). Evidence that mouse brain neuropathy target esterase is a lysophospholipase. Proc. Natl Acad. Set USA 100 7983-7. 

Cholesterol Esters Cholesterol esterase Phospholipids Phospholipase 2 Phospholipase 1 Lysophospholipase... 

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