Phospholipase isozymes

Rhee SG, Bae YS (1997) Regulation of phosphoinositide-specific phospholipase Isozymes. J Biol Chem 272 15045-15048... 

Phosphatidyl inositol, which is present in the inner leaflet of the plasma membrane, is convated to PM,5-bisP by kinases that phosphorylate the inositol ring at the 4 and 5 positions (Fig. 11.12). PM,5-bisP, which has three phosphate groups, is cleaved by a phospholipase C-isozyme to generate IP3 and DAG. The phospholipase isozyme C., (PLC.,) is activated by tyrosine kinase growth factor receptors, and phospholipase C 3 is activated by a heptahelical receptor-G protein signal ffansduction pathway. 

Figure 3. Alignment of proteolytically derived peptides from Solenopsis invicta venom phospholipase (76) with Dolichovespula maculata venom phospholipase isozyme 1 (69). The double dots indicate identical residues and the single dots residues that differ by only a single base (conservative substitutions). Dashes indicate positions inserted to maximize alignment.

Phospholipases. Table 1 Classification of low molecular mass phospholipase A2 isozymes that use catalytic His... 

Phospholipases. Figure 2 Representation ofthe domains in the major isozymes of phospholipase C (adapted from [2]). 

Schaefer U, Schneider A, Rixen D, Neugebauer E (1998) Neutrophil adhesion to histamine stimulated cultured endothelial cells is primarily mediated via activation of phospholipase C and nitric oxide synthase isozymes. Inflamm Res 47(6) 256-264 Schaefer U, Schmitz V, Schneider A, Neugebauer E (1999) Histamine induced homologous and heterologous regulation of histamine receptor subtype mRNA expression in cultured endothelial ceUs. Shock 12(4) 309-315... 

Phosphoinositides are cleaved by a family of phosphoinositide-specific phospholipase C isozymes 350... 

The phospholipases (PLC) isozymes cleave the phosphodiester bond in phos-phatidyl-inositol-4,5-bisphosphate (PIP2) releasing two second messenger molecules inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG) as shown before. The /1-isozyme are controlled by the Ga or G y subunits of the heterotrimeric G-proteins coupled to surface receptors. The y-isozymes are substrates for tyrosine kinases, such as growth factors. 

Selected entries from Methods in Enzymology [vol, page(s)] Phosphatidylinositol-specific phospholipases C from Bacillus ce-reus and Bacillus thuringiensis, 197, 493 assays for phosphoinosi-tide-specific phospholipase C and purification of isozymes from bovine brain, 197, 502 properties of phospholipase C isozymes, 197, 511 phosphatidylinositol-specific phospholipase C from human platelets, 197, 518 purification of guinea pig uterus phos-phoinositide-specific phospholipase C, 197, 526. 

Figure 8.9 Prostaglandins and leukotrienes are potent eicosanoid lipid mediators, derived from phospholipase-released arachidonic acids, that are involved in numerous homeostatic biological functions and inflammation. They are generated by cyclooxygenase isozymes and 5-lipoxygenase, respectively, and their biosynthesis and pharmacological actions are inhibited by clinically relevant nonsteroidal anti-inflammatory drugs.

One of the most studied examples of signaling with membrane lipids is provided by the phospho-inositide cascade, which is pictured in Fig. 11-9. Six or more phosphate esters of phosphatidylinositol (PI) are generated by the action of kinases.219 220 More than 100 extracellular signaling molecules activate specific isozyme forms of phospholipase C,221-224 releasing 20 or more different inositol phosphates from these... 

Hepler JR, Kozasa T, Smrcka AV, Simon MI, Rhee SG, Sternweis PC, Gilman AG (1993) Purification from Sf9 cells and characterization of recombinant Gq alpha and Gil alpha. Activation of purified phospholipase C isozymes by G alpha subunits. J Biol Chem 268(19) 14367-14375... 

Blank, J.L., Ross, A.H., and Exton, J.H. 1991. Purification and characterization of two G-proteins that activate the beta 1 isozyme of phosphoinositide-specific phospholipase C. Identification as members of the Gq class. J. Biol. Chem. 266 18206-18216. 

A third mode of entry of Ca2+ into the cells is mediated by the coupling of the receptor to G proteins. It is believed that this is the pathway used by chemokines. The On reaction begins when the agonist induces a conformational change in the receptor which is transmitted to the G protein. The heterodimeric G protein dissociates into Ga and G 3y subunits, both of which can activate different phospholipase C (PLC) isozymes. This enzyme is able to catalyze the hydrolysis of the lipid precursor phosphatidylinositol 4,5-bisphosphate to give both 1,2-diacylglycerol (DAG) and inositol 1,4,5-trisphosphate (IP3). The latter then binds to the IP3 receptor which mobilizes both stored Ca2+ and promotes an influx of external Ca2+. 

Protein kinase C plays a critical part in the vascular changes associated with diabetes mellitus. It has been proposed that chronic hyperglycemic states begin a cascade of reactions, initially involving the increased tyrosine phosphorylation of phospholipase Cy, which resnlts in elevated levels of diacylglycerol, which then activates protein kinase C. The beta isoform (PKCp) is the predominant isozyme that is activated in vascular tissue... 

For example, an isozyme of glutathione-S-transferase will also catalyze the fatty acid ethyl-ester synthase reaction, leading to the formation of ethyloleate from oleic acid and ethanol (Bora et al. 1989). Also, phospholipase D catalyzes the transphosphatidylation of phosphatidylcholine with ethanol to form phosphatidylethanol (Kobayashi and Kanfer 1987). The active site requirements and kinetics of the hydrolases or transferases that catalyze these ethylation reactions are not well understood. The elucidation of mechanisms and active site structures for enzyme-catalyzed... 

Phospholipase D (PLD) is an enzyme that hydrolyzes phosphohpids, principally phosphatidylchohne (PC), to phosphatidic acid (PA) and the free head group. It is widely distributed and has been purified or cloned from many mammalian, plant, protozoan and bacterial species and also yeasL Drosophila, Anopheles, and C. ele-gans. In mammals it occurs as splice variants of two gene products, and in plants there are multiple genes and isozymes. 

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