Phosphatidylcholine hydrolysis

A more successful strategy for developing sensitive and facile assays to monitor PLCBc activity involves converting the phosphorylated headgroup into a colorimetric agent via a series of enzyme coupled reactions. For example, phosphatidylcholine hydrolysis can be easily monitored in a rapid and sensitive manner by enzymatically converting the phosphorylcholine product into a red dye through the sequential action of alkaline phosphatase, choline oxidase, and peroxidase [33]. This assay, in which 10 nmol of phosphorylcholine can be readily detected, may be executed in a 96-well format and has been utilized in deuterium isotope and solvent viscosity studies [34] and to evaluate inhibitors of PLCBc [33] and site-directed mutants of PLCBc [35,36]. 

Billah, M. M., Eckel, S., Mullmann, T. J., Egan, R. W., Siegel, M. I. (1989). Phosphatidylcholine hydrolysis by phospholipase D determines phosphatidate and diglyceride levels in chemotactic peptide-stimulated human neutrophils. Involvement of phosphatidate phosphohydrolase in signal transduction. J. Biol. Chem. 264, 17069-77. 

Bettaieb, A., Plo, 1., Mansat-de Mas, V., Quillet-Mary, A., Levade, T., Laurent, G., and Jaffrezou, J-P., 1999, Daunorubicin- and Mitoxantrone-tiiggered phosphatidylcholine hydrolysis implication in drug-induced ceramide generation and apoptosis. Mol. Pharm. 55 118-125... 

PHOSPHOLIPASE A2 Phosphatidylcholine 2-acyl hydrolase, PHOSPHOLIPASE A2 Phosphatidylcholine, hydrolysis of, PHOSPHOLIPASE A2 PHOSPHOLIPASE D... 

Cowen DS, Sowers RS, Manning DR. Activation of a mitogen-activated protein kinase (ERK2) by the 5-hydroxytryptamine1A receptor is sensitive not only to inhibitors of phosphatidylinositol 3-kinase, but to an inhibitor of phosphatidylcholine hydrolysis. J Biol Chem 1996 271 22,297-22,300. 

Haas et al. (162) have studied enzymatic phosphatidylcholine hydrolysis in organic solvents by examining selected commercially available lipases. Enzymatic hydrolysis of oat and soy lecithins, and its effect on the functional properties of lecithin, was investigated by Aura et al. (163). The phospholipase used was most effective at low enzyme and substrate concentrations. 

PKC is rapidly activated by a a transient rise in DAG levels resulting from PLC stimulation. Phospholipase D (PLD) causes phosphatidylcholine hydrolysis, which results in an increase in DAG and PKC activity. Phosphatidylinositol 3,4,5-trisphosphate (PIP3), an other lipid metabolite, can activate PKC. 

Gu H, Trajkovic S, Labelle EF. Norepinephrine-induced phosphatidylcholine hydrolysis by phospholipase-D and phospholipase-C in rat tail artery. Am J Physiol 1992 262 C1376-C1383. 

Activation of the a,-ARs causes polyphosphoinositide hydrolysis catalyzed by phospholipase C via pertussis toxin-insensitive G proteins in almost all tissues where this effect has been examined. Recent studies have shown that other signalling pathways can be activated upon a,-AR stimulation such as phosphatidylcholine hydrolysis and phospholipase A2 (for review, see Graham et al., 1996). However, the comparison among different a,-AR-media-ted responses in various tissues has not allowed to assess any conclusive signalling differences among distinct a,-AR subtypes. 

Billah MM, Anthes JC. The regulation and cellular function of phosphatidylcholine hydrolysis. Biochem J 1990 269 281-291. 

T Silberstein. Microemulsion systems as a basis for phosphatidylcholine hydrolysis. PhD thesis, Hebrew University of Jerusalem, Jerusalem, 1999. 

Phosphatidylethanolamine synthesis begins with phosphorylation of ethanol-amine to form phosphoethanolamine (Figure 25.19). The next reaction involves transfer of a cytidylyl group from CTP to form CDP-ethanolamine and pyrophosphate. As always, PP, hydrolysis drives this reaction forward. A specific phosphoethanolamine transferase then links phosphoethanolamine to the diacylglycerol backbone. Biosynthesis of phosphatidylcholine is entirely analogous because animals synthesize it directly. All of the choline utilized in this pathway must be acquired from the diet. Yeast, certain bacteria, and animal livers, however, can convert phosphatidylethanolamine to phosphatidylcholine by methylation reactions involving S-adenosylmethionine (see Chapter 26). 

Fr kjaer et al., 1984 Grit et al., 1989). An example of the pH dependency on the hydrolysis rate of liposomes consisting of soybean phosphatidylcholine is presented in Fig. 6. Hydrolysis kinetics changed rather abruptly around the phase transition temperature. 

Capacitance measurements of phospholipid monolayers at the ITIES have been proposed as a suitable tool for studying the enzyme activity under the precise control of the electrical state of the monolayer [81]. Kinetics of hydrolysis of phosphatidylcholine... 

An important characteristic of mammalian 15-LOX is its capacity to oxidize the esters of unsaturated acid in biological membranes and plasma lipoproteins without their hydrolysis to free acids. Jung et al. [19] found that human leukocyte 15-LOX oxidized phosphatidylcholine at carbon-15 of the AA moiety. Soybean and rabbit reticulocyte 15-LOXs were also active while human leukocyte 5-LOX, rat basophilic leukemia cell 5-LOX, and rabbit platelet 12-LOX were inactive. It was suggested that the oxygenation of phospholipid is a unique property of 15-LOX. However, Murray and Brash [20] showed that rabbit reticulocyte... 

The effect of Li+ upon the synthesis and release of acetylcholine in the brain is equivocal Li+ is reported to both inhibit and stimulate the synthesis of acetylcholine (reviewed by Wood et al. [162]). Li+ appears to have no effect on acetyl cholinesterase, the enzyme which catalyzes the hydrolysis of acetylcholine [163]. It has also been observed that the number of acetylcholine receptors in skeletal muscle is decreased by Li+ [164]. In the erythrocytes of patients on Li+, the concentration of choline is at least 10-fold higher than normal and the transport of choline is reduced [165] the effect of Li+ on choline transport in other cells is not known. A Li+-induced inhibition of either choline transport and/or the synthesis of acetylcholine could be responsible for the observed accumulation of choline in erythrocytes. This choline is probably derived from membrane phosphatidylcholine which is reportedly decreased in patients on Li+ [166],... 

The rate of production of DAG in the cell does not occur linearly with time, but rather it is biphasic. The first peak is rapid and transient and coincides with the formation of IP3 and the release of Ca2+ this DAG is therefore derived from the PI-PLC catalyzed hydrolysis of phosphatidylinositols [1]. There is then an extended period of enhanced DAG production that is now known to be derived from the more abundant phospholipid phosphatidylcholine (PC), which has a different composition of fatty acid side chains [9]. Although DAG may be generated directly from PC through the action of PC-PLC, it can also be formed indirectly from PC. In this pathway, PC is first hydrolyzed by PLD to give choline and phosphatidic acid, which is then converted to DAG by the action of a phos-phatidic acid phosphatase [10,11 ]. 

The length of the acyl side chains of a phosphatidylcholine derivative have significant effects upon the rate with which PLC i( catalyzes the hydrolysis of... 

Table 2. Relative rates of hydrolysis of phosphatidylcholine derivatives by PLC/Ir... 

Several zinc enzymes that catalyse the hydrolysis of phosphoesters have catalytic sites, which contain three metal ions in close proximity (3-7 A from each other). These include (Figure 12.11) alkaline phosphatase, phospholipase C and nuclease PI. In phospholipase C and nuclease PI, which hydrolyse phosphatidylcholine and single-stranded RNA (or DNA), respectively, all three metal ions are Zn2+. However, the third Zn2+ ion is not directly associated with the dizinc unit. In phospholipase C, the Zn-Zn distance in the dizinc centre is 3.3 A, whereas the third Zn is 4.7 and 6.0 A from the other two Zn2+ ions. All three Zn2+ ions are penta-coordinate. Alkaline phosphatase, which is a non-specific phos-phomonoesterase, shows structural similarity to phospholipase C and PI nuclease however,... 

Figure 6.16. Hydrolysis of phosphatidylcholine by phospholipase A2. This reaction yields two important products arachidonic acid and lyso-PAF.

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