Phospholipase activation

Phosphoinositase C (i.e. phosphoinositide-specific phospholipase C [PLC]) enzymes are found in the vast majority of mammalian cells. Molecular cloning of these enzymes, analysis of their predicted amino acid sequences and immunological cross-reactivity indicate that at least three major forms of the enzyme exist PLC-/I, -8 and -y. Each of these enzyme types is encoded by a distinct gene. More recent experiments using the polymerase chain reaction and molecular cloning have revealed even greater enzyme di- 

Neutrophil membranes contain inositol lipids, which comprise about 5-6% of the total membrane lipids. About 80% of these inositol lipids possess stearic acid (Cl8 0) at Cl and arachidonic acid (C20 4) at C2 positions. Phosphatidylinositol accounts for most of these lipids (90%), with smaller amounts of PIP (6%) and PIP 2 (4%), which are synthesised sequentially by the action of 4- and 5-specific kinases, respectively (see Fig. 6.6). Neutrophil membranes also possess a phosphatidylinositol-specific phospholipase C which cleaves phosphatidylinositol 4,5-bisphosphate (PIP2) into Ins 1,4,5 P3 and DAG (Fig. 6.7). Both PLC-/3(/ 2) and PLC-y (72) families appear to be present in neutrophils. The coupling of receptor occupancy to PLC activation in neutrophils can be through a heterotrimeric G-protein, the mobile subunit of which has been termed G p. Evidence for this G-protein link comes from the following facts  

G Op-coupling lowers the apparent affinity of PLC for Ca2+ to about 0.1 - that is, the level found in the cytosol of resting cells. 

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Hanson, D. and De Leo, V.A. (1990). Long-wave ultraviolet light induces phospholipase activation in cultured human epidermal keratinocytes. J. Invest. Dermatol. 95, 158-163. 

FRET probes have not only been generated to measure the phospholipase activity but to study its substrate specificity as well. Several substrates of PLA2 with a variety of head groups and labeled with a BODIPY dye and a Dabcyl quencher were created by Rose et al. and tested against different PLAs in cells to determine substrate specificity and intracellular localization [137], The specificity of PLA2 isoforms towards the number of double bonds in the sn2 position was evaluated with a small series of PENN derivatives. It was demonstrated that the cytosolic type V PLA2 preferred substrates with a single double bond [138],... 

Thompson, N. T., Tateson, J. E., Randall, R. W., Spacey, G. D., Bonser, R. W., Garland, L. G. (1990). The temporal relationship between phospholipase activation, diradyl-glycerol formation and superoxide production in the human neutrophil. Biochem. J. 271, 209-13. 

Watson, F., Robinson, J. J., Edwards, S. W. (1992). Sequential phospholipase activation in the stimulation of the neutrophil NADPH oxidase. FEMS Microbiol. Immunol. 105, 239-48. 

Selected entries from Methods in Enzymology [vol, page(s)] Detergent-resistant phospholipase Ai from Escherichia coll membranes, 197, 309 phospholipase Ai activity of guinea pig pancreatic lipase, 197, 316 purification of rat kidney lysosomal phospholipase Ai, 197, 325 purification and substrate specificity of rat hepatic lipase, 197, 331 human postheparin plasma lipoprotein lipase and hepatic triglyceride lipase, 197, 339 phospholipase activity of milk lipoprotein lipase, 197, 345. 

Effects mediated through stimulation of phospholipase activity and mobilization of intracellular Ca +... 

Wuthier, R. E. The role of phospholipids in biological calcification. Distribution of phospholipase activity in calcifying epiphyseal cartilage. Clin. Orthop. Rel. Res. 90, 191 (1973)... 

Further support for the hypothesis that Ca2+ plays a central role in regulating phytoalexin accumulation is provided by experiments in which the turnover of phosphatidylinositol was measured in the plasma membrane of elicitor-treated carrot cells [17]. The carrot cells were first labelled with [3H]myo-inositol and, after the addition of elicitors, acid extracts of the cells were analyzed chromatographically for the production of inositol trisphosphate (IP3). In cells treated with elicitor, the release of radioactive IP3 increased with time and attained a maximum at 3 - 5 min after treatment. Phospholipase activity responsible for the degradation of phosphorylated phosphatidylinositol increased correspondingly. Several reports have shown that IP3 induces rapid release of Ca2+ from intracellular stores in animal cells [18, 19]. Studies on plant cells have also demonstrated that exogenous IP3 releases Ca2+ from microsomal preparations at micromolar concentrations, although only limited... 

Bernard J., Lahsaini A., and Massicotte G. (1994). Potassium-induced long-term potentiation in area CA1 of the hippocampus involves phospholipase activation. Hippocampus 4 447-453. 

A25. Aron, L, Jones, S., and Fielding, C. J., Human plasma lecithin cholesterol acyltransferase Characterization of cofactor-dependent phospholipase activity. J. Biol. Chem. 253, 7220-7226 (1978). 

Koka, R., Weimer, B. C. 2001. Influence of growth conditions on heat-stable phospholipase activity in Pseudomonas. J. Dairy Res. 68, 109-116. 

In addition to factors, hormones, and neurotransmitters, known to act through receptors that couple to G proteins, Table I also lists effector systems that are or may be affected directly by activated G. Of these effector systems, positive and negative regulation of adenylyl cyclase, activation of phospholipases, activation of cGMP-PDE in photoreceptor cells, and activation of K+ channels are well docu-... 

Jansen SM, Groener JEM, Poorthuis VJHM Lysosomal phospholipase activity is decreased in mucolipidosis II and III fibroblasts. Biochim Biophys Acta 1436 363-369,1999. 

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