Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.4.3 (phospholipase C)
 18,461 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have investigated the topography of a glycosyl-phosphatidylinositol implicated in insulin action by a combination of two complementary methods: (a) chemical labelling with a non-permeable (isethionyl acetimidate) and a permeable (ethyl acetimidate) probe; and (b) enzymatic modifications with beta-galactosidase (EC 3.2.1.23) or phosphatidylinositol-specific phospholipase C (EC 3.1.4.3). Using the first approach the majority of the glycosyl-phosphatidylinositol is found in the outer surface of intact hepatocytes, adipocytes, fibroblasts and lymphocytes, but not in erythrocytes which presented only a 20% of the total labelled glycosyl-phosphatidylinositol to the exterior. Upon insulin addition (10 nM), about 60% of the total glycosyl-phosphatidylinositol was hydrolysed in both hepatocytes and adipocytes but not in erythrocytes. In agreement with the extracellular localization in hepatocytes and with the proposed role of this glycolipid in insulin action, treatment of rat hepatocytes with beta-galactosidase from Escherichia coli, an enzyme that hydrolyses the oligosaccharide moiety of the glycosyl-phosphatidylinositol, cleaved 65% of the total glycophospholipid and blocked the effect of insulin (but not of glucagon) on pyruvate kinase (EC 2.7.1.40). Similar treatment with phosphatidylinositol-specific phospholipase C from Bacillus cereus hydrolysed 62% of the total glycosyl-phosphatidylinositol. From the various approaches used it is concluded that the majority of this glycophospholipid is at the outer surface in a variety of insulin-sensitive cells.
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PMID:Asymmetric distribution of the phosphatidylinositol-linked phospho-oligosaccharide that mimics insulin action in the plasma membrane. 213 37

Smooth muscle was made permeable with alpha-toxin and beta-escin. ATPase activity was measured using a phosphoenolpyruvate-pyruvate kinase regenerating system for ATP that was monitored by NADH fluorescence changes, and Ca2+ was measured using fura 2 fluorescence. alpha-Toxin-and beta-escin-treated bundles of cells had a high ATPase activity, which was reduced 80% when exposed to 1% Triton X-100. This Triton-sensitive ATPase activity was increased by approximately 20% when GTP or GTP gamma S was added to the solutions and was of much greater magnitude than the Ca(2+)-activated ATPase associated with contraction. This high membrane ATPase activity will cause a gradient of ATP into and ADP out of the bundle of cells. Thus modulation of this ATPase by G-protein-receptor mechanisms could alter the force at a constant Ca2+ concentration by changing the ADP/ATP ratio within the cells. Measurements of the fura 2 fluorescence ratio (340/380) in alpha-toxin-treated bundles of cells following sudden changes in extracellular Ca2+ showed that the cells were not freely permeable to Ca EGTA. Similar experiments in beta-escin-treated cells showed the cells to be much more permeable to Ca EGTA. These experiments indicate that great care must be taken in alpha-toxin- and beta-escin-treated fibers to make sure that the intracellular ATP, ADP, and Ca2+ are held constant.
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PMID:Relationship between ATPase activity, Ca2+, and force in alpha-toxin- and beta-escin-treated smooth muscle. 776 79

The efflux of lactate dehydrogenase and haemoglobin from human erythrocytes during prolonged incubation at 37 degrees was significantly reduced by ATP, ADP, AMP, UTP, creatine phosphate, or phosphoenolpyruvate and to a lesser extent by fructose, glucose 6-phosphate or fructose 6-phosphate, but not by glucose. Iodoacetate, however, markedly increased the loss of haemoglobin and slightly increased that of lactate dehydrogenase. Phospholipase C greatly accelerated the relase of haemoglobin, lactate dehydrogenase, pyruvate kinase, hexokinase, glucose 6-phosphate dehydrogenase, and 6-phosphogluconate dehydrogenase from human erythrocytes, but this effect was also reduced in the presence of ATP or ADP. The loss of lactate dehydrogenase, malate dehydrogenase, and pyruvate kinase from the cells treated with phospholipase C increased as their ATP content fell. In a series of experiments in which the action of phospholipase C was stopped by the subsequent addition of trypsin, ATP and ADP (1 mmol/l) significantly reduced the efflux of haemoglobin, but AMP had no such effect. The results are consistent with the conclusion from our previous work that enzyme leakage is related to diminution in the energy content of the cells. The protective action of AMP on cells not treated with phospholipase C, however, differs from earlier findings with rat lymphocytes and it is suggested that in red cells it might be converted into ATP or that it has a direct effect on the permeability of the cell membrane.
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PMID:Factors affecting the release of haemoglobin and enzymes from human erythrocytes. 1563 25

Although glucocorticoids are widely used as antiinflammatory agents in clinical therapies, they may cause serious side effects that include insulin resistance and hyperinsulinemia. To study the potential functional adaptations of the islet of Langerhans to in vivo glucocorticoid treatment, adult Wistar rats received dexamethasone (DEX) for 5 consecutive days, whereas controls (CTL) received only saline. The analysis of insulin release in freshly isolated islets showed an enhanced secretion in response to glucose in DEX-treated rats. The study of Ca(2+) signals by fluorescence microscopy also demonstrated a higher response to glucose in islets from DEX-treated animals. However, no differences in Ca(2+) signals were found between both groups with tolbutamide or KCl, indicating that the alterations were probably related to metabolism. Thus, mitochondrial function was explored by monitoring oxidation of nicotinamide dinucleotide phosphate autofluorescence and mitochondrial membrane potential. Both parameters revealed a higher response to glucose in islets from DEX-treated rats. The mRNA and protein content of glucose transporter-2, glucokinase, and pyruvate kinase was similar in both groups, indicating that changes in these proteins were probably not involved in the increased mitochondrial function. Additionally, we explored the status of Ca(2+)-dependent signaling kinases. Unlike calmodulin kinase II, we found an augmented phosphorylation level of protein kinase C alpha as well as an increased response of the phospholipase C/inositol 1,4,5-triphosphate pathway in DEX-treated rats. Finally, an increased number of docked secretory granules were observed in the beta-cells of DEX animals using transmission electron microscopy. Thus, these results demonstrate that islets from glucocorticoid-treated rats develop several adaptations that lead to an enhanced stimulus-secretion coupling and secretory capacity.
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PMID:Glucocorticoids in vivo induce both insulin hypersecretion and enhanced glucose sensitivity of stimulus-secretion coupling in isolated rat islets. 1988 Aug 8