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

---

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

Activation of Ca2+-mobilizing receptors rapidly increases the cytoplasmic Ca2+ concentration both by releasing Ca2+ stored in endoplasmic reticulum and by stimulating Ca2+ entry into the cells. The mechanism by which Ca2+ release occurs has recently been elucidated. Receptor activation of phospholipase C results in the hydrolysis of the plasma membrane lipid, phosphatidylinositol 4,5-bisphosphate (PIP2), to yield two intracellular messengers, diacylglycerol (DAG) and (1,4,5)inositol trisphosphate [(1,4,5)IP3]. DAG remains in the plasma membrane where it stimulates protein phosphorylation via the phospholipid-dependent protein kinase C. (1,4,5)IP3 diffuses to and interacts with specific sites on the endoplasmic reticulum to release stored Ca2+. Receptor stimulation of phospholipase C appears to be mediated by one or more guanine nucleotide-dependent regulatory proteins by a mechanism analogous to hormonal activation of adenylyl cyclase. The actions of (1,4,5)IP3 on Ca2+ mobilization are terminated by two metabolic pathways, sequential dephosphorylation to inositol bisphosphate (IP2), inositol monophosphate (IP) and inositol or by phosphorylation to inositol tetrakisphosphate (IP4) and sequential dephosphorylation to different inositol phosphates. A sustained cellular response also requires Ca2+ entry into the cell from the extracellular space. The mechanism by which hormones increase Ca2+ entry is not known; a recent proposal involving movement of Ca2+ through the endoplasmic reticulum, possibly regulated by IP4, will be considered here.
...
PMID:Metabolism and functions of inositol phosphates. 307 38

1. Activation of vascular smooth muscle by angiotensin II results in the generation of two second messengers, inositol trisphosphate (IP3) and diacylglycerol (DG). 2. IP3 is responsible for mobilizing calcium from endoplasmic reticulum. This signal is transient, most likely serving to initiate calcium events leading to contraction, and is attenuated by activation of protein kinase C. 3. DG stimulates protein kinase C and ultimately Na+/H+ exchange, leading to intracellular alkalinization. Accumulation of DG/activation of protein kinase C is sustained, and may be enhanced by concurrent intracellular alkalinization. The delay in induction of the sustained response appears to be related to cellular processing of the angiotensin II-receptor complex. 4. Angiotensin II-stimulated, phospholipase C-mediated IP3 formation is also modulated by a pertussis toxin-insensitive guanine nucleotide regulatory protein. 5. The GTP binding protein, movement of the receptor-ligand complex, and the signals generated by the two second messengers, IP3 and DG, interact in a complex manner to cause an integrated response of vascular smooth muscle cells to angiotensin II stimulation.
...
PMID:Secondary signalling mechanisms in angiotensin II-stimulated vascular smooth muscle cells. 307 71

The initial events in signal transduction in insulin-secreting cells are summarized in FIGURE 8. Both nutrient stimuli, such as glucose and amino acids and the muscarinic agonist carbachol (carbamylcholine) raise [Ca2+]i. Although the rise in [Ca2+]i precedes the stimulation of insulin release, it is not a moment-to-moment regulator of release. The metabolizable fuel stimuli cause Ca2+ influx through voltage-dependent Ca2+ channels following depolarization of the membrane potential. In contrast, carbachol, which does not depolarize, elicits Ptd Ins 4,5-P2 hydrolysis, a reaction catalyzed by phospholipase C. The generation of Ins 1,4,5-P3 in this instance is Ca2+ independent, but appears to involve a GTP-binding protein. However, this protein is not a substrate for pertussis toxin. The levels of Ins 1,4,5-P3, which releases Ca2+ from an ATP-dependent Ca2+ pool of the endoplasmic reticulum, are increased prior to the rise in [Ca2+]i. The mitochondria may take up Ca2+ after large increases in [Ca2+]i. A previously proposed second messenger, arachidonic acid, is much less selective than Ins 1,4,5-P3 in that it releases Ca2+ from mitochondria as well as from the endoplasmic reticulum in a slow and irreversible manner. As Ins 1,4,5-P3 is also generated during glucose stimulation of islets, albeit in a Ca2+-dependent manner, this metabolite could mediate not only the action of carbachol but also contribute to amplifying the [Ca2+]i rise in response to glucose.
...
PMID:Signal transduction in insulin secretion: comparison between fuel stimuli and receptor agonists. 310 54

Bilirubin UDP-glucuronyltransferase displays marked latency in native microsomes. To examine whether this latency correlates with structural integrity of the microsomal vesicles and reflects lumenal orientation of the enzyme's catalytic center, we analyzed the relationship between transferase activity and the degree of expression of mannose (Man)-6-phosphatase, which is a marker enzyme of the cisternal face of the ER membrane. Using detergent, sonication, or the pore-forming Staphylococcus aureus alpha-toxin to breach the microsomal membrane permeability barrier, we found that after each of these pretreatments a remarkably close direct relationship existed between latency changes for bilirubin UDP-glucuronyltransferase and Man-6-phosphatase. This finding suggested that the transferase may have the same transverse topology as the phosphohydrolase. We also compared the effects of membrane-impermeant proteinases on bilirubin UDP-glucuronyltransferase activity in native and disrupted microsomes. Whereas the unspecific proteinase nagarse markedly inactivated (to less than 30% of activities in controls) the transferase in disrupted microsomes, treatment with the proteinase had little effect on transferase activity in sealed microsomal vesicles. The results suggest that the active site of bilirubin UDP-glucuronyltransferase is on the lumenal face of the endoplasmic reticulum membrane. It was also found that activation of transferase activity by UDP N-acetylglucosamine, which is the presumed allosteric effector of UDP-glucuronyltransferase, was markedly altered by relatively small changes in structural integrity of the microsomes and totally abolished when latency of Man-6-P hydrolysis fell below approximately 80%. Collectively, these findings demonstrate that the microsomal membrane permeability barrier is a major determinant of expression of microsomal UDP-glucuronyltransferase activity and that quantitative assessment of integrity of the microsomes is essential for studying kinetic properties and regulation of microsomal UDP-glucuronyltransferase.
...
PMID:Topology and regulation of bilirubin UDP-glucuronyltransferase in sealed native microsomes from rat liver. 313 Aug 1

Cell activation of different cell types is accompanied by receptor-mediated stimulation of phospholipase C and a consequent breakdown of phosphatidylinositol 4,5-bisphosphate. Evidence suggests that GTP-binding proteins are involved in this signal transduction mechanism, which couples receptors to phospholipase C. Both the hydrolysis products diacylglycerol (DG) and inositol 1,4,5-trisphosphate (IP3) are intracellular messengers for cellular responses such as secretion, as illustrated by the pancreatic acinar cell. IP3 releases Ca2+ from a nonmitochondrial Ca2+ pool likely to be the endoplasmic reticulum (ER). This Ca2+ release leads to a transient rise in the cytosolic free Ca2+ concentration from approximately 100 to approximately 800 nmol/liter, by which enzyme secretion is initiated. For sustained secretion, Ca2+ influx into the cell is necessary to keep the cytosolic free Ca2+ concentration at a slightly elevated level. Activation of protein kinase C by DG and Ca2+ seems to play a major role in the second, sustained phase of secretion. Ca2+ reuptake into the ER and Ca2+ extrusion from the cell are achieved by (Ca2+ + Mg2+)-ATPase in both the ER and the plasma membrane as well as by an Na+/Ca2+ exchange in the latter. In the final step of exocytosis, protein phosphorylation by Ca2+-, DG-, and cAMP-dependent protein kinases is probably involved.
...
PMID:The role of phosphatidylinositides in stimulus-secretion coupling in the exocrine pancreas. 314 61

Trypanosome variant surface glycoproteins (VSGs) have a novel glycan-phosphatidylinositol membrane anchor, which is cleavable by a phosphatidylinositol-specific phospholipase C. A similar structure serves to anchor some membrane proteins in mammalian cells. Using kinetic and ultrastructural approaches, we have addressed the question of whether this structure directs the protein to the cell surface by a different pathway from the classical one described in other cell types for plasma membrane and secreted glycoproteins. By immunogold labeling on thin cryosections we were able to show that, intracellularly, VSG is associated with the rough endoplasmic reticulum, all Golgi cisternae, and tubulovesicular elements and flattened cisternae, which form a network in the area adjacent to the trans side of the Golgi apparatus. Our data suggest that, although the glycan-phosphatidylinositol anchor is added in the endoplasmic reticulum, VSG is nevertheless subsequently transported along the classical intracellular route for glycoproteins, and is delivered to the flagellar pocket, where it is integrated into the surface coat. Treatment of trypanosomes with 1 microM monensin had no effect on VSG transport, although dilation of the trans-Golgi stacks and lysosomes occurred immediately. Incubation of trypanosomes at 20 degrees C, a treatment that arrests intracellular transport from the trans-Golgi region to the cell surface in mammalian cells, caused the accumulation of VSG molecules in structures of the trans-Golgi network, and retarded the incorporation of newly synthesized VSG into the surface coat.
...
PMID:Intracellular transport of a variant surface glycoprotein in Trypanosoma brucei. 333 91

Rats treated with a single 0.5 ml/kg dose (ip) of CCl4 exhibited a threefold increase in liver microsomal phospholipase C (PLC) activity that was enhanced by phenobarbital and diminished by metyrapone pretreatment, respectively. Hepatocytes and hepatocellular fractions exposed to 0.5 mM CCl4 in vitro also exhibited a rapid rise in PLC activity that was reduced by metyrapone. Metyrapone also reduced the CCl4-related increase in the PLC-mediated reductions in cellular phosphatidylcholine content. The influence of CCl4 biotransformation on the activation of liver cell PLC was assessed in vitro. Covalent binding of 14CCl4 metabolites to isolated hepatocyte proteins and lipids was linear through 20 min of incubation and then quickly plateaued. The association of CCl4 metabolites with cellular phospholipids was inhibited by metyrapone and preceded the CCl4-dependent rise in PLC activity. CCl4-mediated increases in PLC activity were rapid and preceded reductions in cell viability. The translocation of cytosolic PLC to membranes such as the endoplasmic reticulum may explain the rapid, metabolite-dependent activation of PLC.PLC activation by haloalkanes was proportional to dose and incubation time in the order of CBrCl3 greater than CCl4 greater than CHCl3 greater than CFCl3 which corresponds to the observed hepatotoxic potential of these agents in vivo and in vitro. Haloalkane-dependent increases in PLC activity were inhibited by metyrapone. These results suggest that chemical metabolites activate PLC in vitro and in vivo. Therefore, the activation of a PLC that degrades membrane phospholipids may represent an important step in the pathogenic scheme of chemical-mediated liver cell necrosis.
...
PMID:The role of CCl4 biotransformation in the activation of hepatocyte phospholipase C in vivo and in vitro. 342 Jun 13

An ultrastructural examination of cultured bovine chromaffin cells permeabilized with Staphylococcus aureus alpha-toxin or digitonin revealed differences in the preservation of cell morphology. The toxin-treated cells closely resembled control cultured cells whereas digitonin-treated cells showed gradations in cytoplasmic densities suggesting extraction, some swelling of the endoplasmic reticulum and, occasionally, discontinuities in the plasma membrane and free granules in the extracellular medium. In both cell models, there was a swelling of the mitochondria. Horseradish peroxidase labelling of permeabilized cells marked the cytoplasm of digitonin-treated cells but only the surface of toxin-treated cells, demonstrating that larger lesions were caused by digitonin. In stimulated cells, the decrease in volumetric density of chromaffin granules correlated well with catecholamine release. The sites of secretory activity could be demonstrated in toxin-treated cells using horseradish peroxidase as a surface marker. Although both cell systems secrete catecholamines in response to calcium stimulation, their calcium requirements and the kinetics of release were different. In alpha-toxin-treated cells, 100 microM free calcium induced maximal catecholamine release. In digitonin-treated cells, 20 microM evoked maximal release but secretion was blocked at 100 microM. Catecholamine release terminated in digitonin-treated cells within 10 min but continued in alpha-toxin-treated cells for at least 60 min. In addition, the maximal release observed in toxin-treated cells (50%) was always greater than that observed in digitonin-permeabilized cells (20%). The results suggest that both exocytosis and granule translocation are operational in alpha-toxin-treated cells, but that the translocation step or the docking of granules at the plasma membrane may be impaired in digitonin-treated cells.
...
PMID:Morphology and secretory activity of digitonin- and alpha-toxin-permeabilized chromaffin cells. 343 93

The neural cell adhesion molecule (N-CAM) of rodents comprises three distinct proteins of Mr 180,000, 140,000, and 120,000 (designated N-CAM-180, -140, and -120). They are expressed in different proportions by different tissues and cell types. but the individual contribution of each form to cell adhesion is presently unknown. Previous studies have shown that the two N-CAM species of higher relative molecular mass span the membrane whereas N-CAM-120 lacks a transmembrane domain and can be released from the cell surface by phosphatidylinositol-specific phospholipase C. In this report, we provided evidence that N-CAM-120 contained covalently bound phosphatidylinositol and studied N-CAM-120 from its biosynthesis to its membrane insertion and finally to its release from the cell surface. Evidence was presented showing that the lipid tail of N-CAM-120 contained ethanolamine as is the case for other lipid-linked molecules. The phospholipid anchor was attached to the protein during the first minutes after completion of the polypeptide chain. This process took place in the endoplasmic reticulum as judged from endoglycosidase H digestion experiments. Immediately after a 2-min pulse with [35S]methionine, we detected also a short-lived precursor that had not yet acquired the lipid tail. Pulse-chase studies established that N-CAM-120 was transported to the cell surface from which it was slowly released into the extracellular milieu. The molecules recovered in the incubation medium appeared to have lost all of their bound fatty acid but only around half of the ethanolamine. Upon fractionation of brain tissue, approximately 75% of N-CAM-120 was recovered with a membrane fraction and approximately 25% in a membrane-free supernatant. A small proportion (approximately 6%) was found to be resistant to extraction by non-ionic detergent. A major posttranslational modification of N-CAM is polysialylation. Our results showed that also N-CAM-120 was polysialylated in the young postnatal brain and released in this form from cultured cerebellar cells. The presence of N-CAM in a form that can be released from the cell surface and accumulates in the extracellular fluid suggests a novel mechanism by which N-CAM-mediated adhesion may be modulated.
...
PMID:Biosynthesis, membrane association, and release of N-CAM-120, a phosphatidylinositol-linked form of the neural cell adhesion molecule. 369 91

Previous attempts in several laboratories, including ours, to purify oligosaccharyl-transferase have met with limited success because of the lability of the membrane-associated enzyme after solubilization with detergents. In an effort to identify the enzyme in face of this lability, we recently developed a photoaffinity reagent to label the active site [J. K. Welply, P. Shenbagamurthi, F. Naider, H. R. Park, and W. J. Lennarz (1985) J. Biol. Chem. 260, 6459-6465]. In this report, the preparations of a more sensitive selective labeling probe, 125I-labeled N alpha-3-(4-hydroxyphenylpropionyl)-Asn-Lys-(N epsilon-p-azidobenzoyl)-Thr-NH2, is described. Using this new probe, we have confirmed, independently of catalytic activity, that hen oviduct oligosaccharyltransferase is tightly associated with the endoplasmic reticulum membrane. The 125I-labeled oligosaccharyltransferase was released from the membrane by detergent and strong alkali treatments but not by sonication, high salt, or hypotonic shock. However, all procedures that released the enzyme from the membrane resulted in a dramatic loss of enzyme activity. Treatment of sealed microsomal membrane vesicles with phospholipase A resulted in nearly complete enzyme inactivation; in contrast, phospholipase C or D had moderate or little effect, respectively. Taken together, these results suggest that the hydrophobic environment of the membrane is required for oligosaccharyltransferase activity. Trypsin treatment of intact vesicles diminished enzyme activity by nearly 70%, but it had no effect on the binding affinity of the enzyme for the 125I-labeled photoaffinity probe. This result suggests that the polypeptide acceptor portion of oligosaccharyltransferase is lumenally disposed, and that a trypsin-sensitive, cytoplasmically oriented domain or another subunit binds the carbohydrate donor, dolichol-PP-oligosaccharide.
...
PMID:Studies on properties of membrane-associated oligosaccharyltransferase using an active site-directed photoaffinity probe. 370 33


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---