Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.1.4.3 (phospholipase C)
18,461 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The role of phospholipids in the binding of 125I-choriogonadotropin to bovine corpus luteum plasma membranes has been investigated with the use of purified phospholipase A and phospholipase C to alter membrane phospholipids. The phospholipase C-digested plasma membrane preparation showed 85 to 90% inhibition of 125I-choriogonadotropin binding activity when 70% of the membrane phospholipid was hydrolyzed. Similarly treatment of plasma membranes with phospholipase A resulted in 45 to 55% hydrolysis of membrane phospholipid and almost 75% inhibition of receptor activity. Both these enzymes hydrolyzed membrane-associated phosphatidylcholine to a greater extent than phosphatidylethanolamine and phosphatidylserine. Phosphorylaminoalcohols of phospholiphase C end products were completely released into the medium, while phospholipase A by-products remained associated with plasma membranes. Addition of a phospholipids suspension or liposomes to plasma membranes pretreated with phospholipase A and C did not restore gonadotropin binding activity. Soluble phosphorylcholine, phosphorylethanolamine, and phosphorylserine and insoluble diglyceride products of phospholipase C action had no effect on receptor activity. In contrast, end products of the phospholipase A action, such as lysophosphatides and fatty acids, inhibited both on the membrane-associated and solubilized receptor activity. Lysophosphatidylcholine was the most effective end product inhibiting the binding of gonadotropin to the receptor, followed by lysophosphatidylethanolamine and lysophosphatidylserine. The inhibitory effects of phospholipase A or lysophosphatides were completely reversed upon removal of membrane-bound phospholipid end products by washing the membranes with defatted bovine serum albumin. However, phospholipase C inhibition could not be overcome by defatted albumin washings. Solubilization of plasma membranes with detergents which had been pretreated with phospholipase C partially restored the inhibited activity. It is concluded that the phospholipase-mediated inhibition of gonadotropin binding activity was due to hydrolysis and alterations of the phospholipid environment in the case of phospholipase C and by direct inhibition by end products in the case of phospholipase A.
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PMID:Gonadotropin receptors in plasma membranes of bovine corpus luteum. II. Role of membrane phospholipids. 18 86

The interaction of the lecithin molecule fragments and their analogues with phospholipase C Cl. perfringens was studied by gel-diffusion in agarose-lecithin gels. It was found intense inhibition of phospholipase C activity in the presence of cathionic compounds; this phenomenon shows the existence of anionic centre in the active site of enzyme. The esteric centre is probably hydrophobic nature and is not capable to bind the negatively charged groups. However, phosphoserine, phosphothreonine, gamma-aminobutyric, aspartic and glutamic acids can interact with an additional cathionic centre, whose location in phospholipase C differs from that in pancreatic phospholipase A2.
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PMID:[The actions of low-molecular fragments of substrate and their analogs on the activity of isoenzymes of phospholipase C from Clostridium perfringens]. 19 87

The hydrolysis of phosphatidylinositol 4,5-bisphosphate has a central role in many signalling pathways. One of the phospholipase C (PLC) isozymes that mediates this reaction is a direct substrate for the tyrosine kinase activity of several growth factor receptors. Growth factors elicit increases in both the phosphoserine and the phosphotyrosine content of the PLC-gamma 1 isozyme. PLC-gamma 1 contains three tyrosine phosphorylation sites, which have been identified as residues 771, 783 and 1254. Phosphorylation of tyrosine residues is sufficient to increase the catalytic activity of PLC-gamma 1, though other proteins may modulate this activation. However, the role of growth factor-enhanced phosphorylation of serine residues on PLC-gamma 1 remains obscure. In vitro studies of PLC-gamma 1, recovered from growth factor-treated cells, indicate that activation by tyrosine phosphorylation is not due to increased sensitivity to Ca2+, a required co-factor, but is reflected in altered kinetic constants, i.e. V(max) and, to a lesser extent, Km.
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PMID:Growth factor phosphorylation of PLC-gamma 1. 139 33

Alkaline phosphatase was the first zinc enzyme to be discovered in which three closely spaced metal ions (two Zn ions and one Mg ion) are present at the active center. Zn ions at all three sites also produce a maximally active enzyme. These metal ions have center-to-center distances of 3.9 A (Zn1-Zn2), 4.9 A (Zn2-Mg3), and 7.1 A (Zn1-Mg3). Despite the close packing of these metal centers, only one bridging ligand, the carboxyl of Asp51, bridges Zn2 and Mg3. A crystal structure at 2.0-A resolution of the noncovalent phosphate complex, E.P, formed with the active center shows that two phosphate oxygens form a phosphate bridge between Zn1 and Zn2, while the two other phosphate oxygens form hydrogen bonds with the guanidium group of Arg166. This places Ser102, the residue known to be phosphorylated during phosphate hydrolysis, in the required apical position to initiate a nucleophilic attack on the phosphorous. Extrapolation of the E.P structure to the enzyme-substrate complex, E.ROPO4(2-), leads to the conclusion that Zn1 must coordinate the ester oxygen, thus activating the leaving group in the phosphorylation of Ser102. Likewise, Zn2 appears to coordinate the ester oxygen of the seryl phosphate and activate the leaving group during the hydrolysis of the phosphoseryl intermediate. Both of these findings suggest that there may be a significant dissociative character to each of the two displacements at phosphorous catalyzed by alkaline phosphatase. A water molecule (or hydroxide) coordinated to Zn1 following formation of the phosphoseryl intermediate appears to be the nucleophile in the second step of the mechanism. Dissociation of the product phosphate from the E.P intermediate is the slowest, 35 s-1, and therefore the rate-limiting, step of the mechanism at alkaline pH. Since the determination of the initial crystal structure of alkaline phosphatase, two other crystal structures of enzymes involved in phosphate ester hydrolysis have been completed that show a triad of closely spaced zinc ions present at their active centers. These enzymes are phospholipase C from Bacillus cereus (structure at 1.5-A resolution) (43) and P1 nuclease from Penicillium citrinum (structure at 2.8-A resolution) (74). Both enzymes hydrolyze phosphodiesters. Substrates for phospholipase C are phosphatidylinositol and phosphatidylcholine, while P1 nuclease is an endonuclease hydrolyzing single stranded ribo- and deoxyribonucleotides. P1 nuclease also has activity as a phosphomonoesterase against 3'-terminal phosphates of nucleotides. The Zn ions in both enzymes form almost identical trinuclear sites.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Structure and mechanism of alkaline phosphatase. 152 73

Because functionally significant substrates for the tyrosyl protein kinase activity of pp60v-src are likely to include membrane-associated proteins involved in normal growth control, we have tested the hypothesis that pp60v-src could phosphorylate and alter the signaling activity of transmembrane growth factor receptors. We have found that the epidermal growth factor (EGF) receptor becomes constitutively phosphorylated on tyrosine in cells transformed by the src oncogene and in addition displays elevated levels of phosphoserine and phosphothreonine. High-performance liquid chromatography phosphopeptide mapping revealed two predominant sites of tyrosine phosphorylation, both of which differed from the major sites of receptor autophosphorylation; thus, the src-induced phosphorylation is unlikely to occur via an autocrine mechanism. To determine whether pp60v-src altered the signaling activity of the EGF receptor, we analyzed the tyrosine phosphorylation of phospholipase C-gamma, since phosphorylation of this enzyme occurs in response to activation of the EGF receptor but not in response to pp60v-src alone. We found that in cells coexpressing pp60v-src and the EGF receptor, phospholipase C-gamma was constitutively phosphorylated, a result we interpret as indicating that the signaling activity of the EGF receptor was altered in the src-transformed cells. These findings suggest that pp60v-src-induced alterations in phosphorylation and function of growth regulatory receptors could play an important role in generating the phenotypic changes associated with malignant transformation.
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PMID:Phosphorylation and activation of epidermal growth factor receptors in cells transformed by the src oncogene. 170 13

The mechanism by which cAMP modulates the activity of phosphoinositide-specific phospholipase C (PLC) was studied. Elevation of cAMP inhibited both basal and norepinephrine-stimulated phosphoinositide breakdown in C6Bu1 cells which contain at least three PLC isozymes, PLC-beta, PLC-gamma, and PLC-delta. Treatment of C6Bu1 cells with cAMP-elevating agents (cholera toxin, isobutylmethylxanthine, forskolin, and 8-bromo-cAMP) increased serine phosphate in PLC-gamma, but the phosphate contents in PLC-beta and PLC-delta were not changed. In addition, cAMP-dependent protein kinase selectively phosphorylated purified PLC-gamma among the three isozymes and added a single phosphate at serine. The serine phosphorylation, nevertheless, did not affect the activity of PLC-gamma in vitro. We propose, therefore, that the phosphorylation of PLC-gamma by cAMP-dependent protein kinase alters its interaction with putative modulatory proteins and leads to its inhibition.
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PMID:Phosphorylation of phospholipase C-gamma by cAMP-dependent protein kinase. 247 46

Although IL-1 stimulates cellular responses in both lymphoid and nonlymphoid cells, the second messengers by which IL-1 activates cells are unknown. Recombinant IL-1 alpha (rIL-1) is a comitogen for glomerular mesangial cells. Using this model we explored potential transmembrane signals by which IL-1 stimulates cellular responses. Certain mitogens hydrolyze inositol phospholipids by phospholipase C to generate 1,2-diacylglycerol, a cofactor for protein kinase C, and inositol (1,4,5)-trisphosphate, which mobilizes intracellular calcium. rIL-1 induced a peak increase in [3H]1,2-diacylglycerol formation at 1 min. Production of 1,2-diacylglycerol often parallels the generation of phosphatidic acid; however, rIL-1 stimulated [32P]phosphatidate formation only after 60 min. rIL-1 did not change the inositol phosphate or cytosolic free calcium concentrations, demonstrating that rIL-1 does not activate an inositol phospholipid-specific phospholipase C. [3H]Phosphorylethanolamine, but not [3H]phosphorylserine or [3H]phosphorylcholine, was maximally elevated at 1 min in mesangial cells incubated with rIL-1. Radioactivity incorporated into phosphatidylethanolamine but not phosphatidylcholine was also decreased in IL-1-stimulated mesangial cells compared with control at 1 min. These data suggest that rIL-1 activates a phospholipase C predominantly linked to phosphatidylethanolamine. In contrast to other mitogens, rIL-1 did not alter intracellular pH. Both 12-0-tetradecanoyl-phorbol-13-acetate, a homologue of 1,2-diacylglycerol, and phosphatidate but not phosphatidylcholine in the presence of 0.5% fetal bovine serum stimulated mesangial cell proliferation. rIL-1-induced cellular activation may be mediated, at least in part, by phospholipid-derived second messengers generated through novel pathways.
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PMID:Interleukin-1 generates transmembrane signals from phospholipids through novel pathways in cultured rat mesangial cells. 278 92

Addition of isoproterenol to isolated rat adipocytes prelabeled with [32P]phosphate caused an increase in the phosphorylation and activation of phospholipid methyltransferase. 32P-Labeled phospholipid methyltransferase was recovered by immunoprecipitation and gel electrophoresis. Analysis of 32P-labeled peptides revealed one site of phosphorylation regulated by isoproterenol, and analysis of phosphoamino acids demonstrated that the incorporation of [32P]phosphate was on phosphoserine. Incubation of adipocytes with isoproterenol in the presence of insulin or a phospho-oligosaccharide inhibited the phosphorylation and activation of this enzyme. The inhibitory effect of insulin on the phosphorylation of phospholipid methyltransferase was reversible, and it was mimicked by a phospho-oligosaccharide. The phospho-oligosaccharide was generated by hydrolysis of an isolated glycophospholipid with phosphatidylinositol-specific phospholipase C from Staphylococcus aureus. The insulin-like effect of this phospho-oligosaccharide on the phosphorylation of phospholipid methyltransferase was demonstrated in isolated adipocytes, and the effect was abolished by treatment of the phospho-oligosaccharide with 10% NH4OH, nitrous acid, or sodium periodate. These data suggest that in intact adipocytes the effect of insulin to inhibit the phosphorylation/activation of phospholipid methyltransferase is mediated by a phospho-oligosaccharide generated by a phosphatidylinositol-specific phospholipase C.
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PMID:A phospho-oligosaccharide mimics the effect of insulin to inhibit isoproterenol-dependent phosphorylation of phospholipid methyltransferase in isolated adipocytes. 331 3

Angiotensin II AT1 receptor signal transduction has recently been shown to function through the phospholipase C isozyme, PLC-gamma. Since PLC-gamma is known to interact with phosphotyrosine containing proteins through SH2 domains, we examined the phosphorylation state of the AT1 receptor. Immunoprecipitation of the [32P] labeled AT1 receptor from rat aortic smooth muscle cells followed by alkali hydrolysis demonstrated the presence of tyrosine phosphorylation. Phosphoamino acid analysis of the excised bands demonstrated the presence of phosphoserine and phosphotyrosine residues. A fusion protein comprising the intracellular tail of the AT1 receptor was used to screen for candidate kinases, and the src kinase family displayed high activity. In summary, this study shows that the AT1 receptor is serine and tyrosine phosphorylated in vivo and suggests that a soluble kinase related to the src family may be responsible for the tyrosine phosphorylation.
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PMID:The angiotensin II AT1 receptor is tyrosine and serine phosphorylated and can serve as a substrate for the src family of tyrosine kinases. 751 59

Epidermal growth factor (EGF) stimulates phosphatidylinositol PtdIns) hydrolysis in many cell types by effecting the specific interaction between the EGF receptor and phospholipase C gamma. Several studies have suggested that PtdIns 4-kinase activity can also be regulated by EGF, but the mechanism of this stimulation was unclear. We report here that EGF treatment of intact A431 cells increased the association of type II PtdIns kinase with the EGF receptor within 1 min at 37 degrees C. Phosphorylation of immunoprecipitated EGF receptor also increased the association of PtdIns 4-kinase. Furthermore dephosphorylation of phosphoserine residues on the stimulated receptor immune complex led to inactivation of the bound PtdIns 4-kinase, while dephosphorylation of phosphotyrosine residues led to activation. Unlike the stimulated activity measured in total cell and plasma membrane lysates, the changes in activity of the immunoprecipitates were apparent at high substrate concentration. Metabolic labeling was used to show that a 55-kDa phosphoserine and phosphotyrosine-containing protein comigrated with renatured PtdIns 4-kinase activity on SDS-polyacrylamide gel electrophoresis, while in vitro labeling revealed only serine phosphorylation. These data are discussed with reference to the direct regulation of PtdIns 4-kinase by phosphorylation, PtdIns compartmentalization, and the formation of a multienzyme signal transduction complex.
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PMID:Regulation of human type II phosphatidylinositol kinase activity by epidermal growth factor-dependent phosphorylation and receptor association. 798 68


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