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)

The salivary glands of adult blowflies (Calliphora erythrocephala) contain enzymes that hydrolyse phosphatidylinositol, predominantly by a Ca2+-independent deacylation, though a Ca2+-dependent phosphodiesterase (phospholipase C) activity could be detected. The deacylating enzymes could also hydrolyse phosphatidylcholine and phosphatidylethanolamine, and were secreted in the saliva. Homogenization of salivary glands prelabelled with [3H]inositol resulted in a rapid deacylation of the endogenous 3H-labelled phosphatidylinositol; this hydrolysis was unaffected by addition of 5-hydroxytryptamine to the homogenate.
 ...
PMID:Phosphatidylinositol-hydrolysing enzymes in blowfly salivary glands. 628 18

1. The Ca(2+)-dependent phosphatidylinositol phosphodiesterase (phospholipase C-type) from the cytosolic supernatant of rat brain was active against exogenous [(32)P]-phosphatidylinositol from pH5.0 to pH8.5. However, the activity in the range pH7.0-8.5 could not be recovered after precipitation with (NH(4))(2)SO(4); most of the enzyme activity was recovered in the 30-50% fraction and showed a single sharp pH optimum at 5.5. 2. The cytosolic supernatant was analysed by isoelectric focusing on acrylamide gels, and assay at pH5.5. Four peaks of phosphodiesterase activity were found at pI ranges 7.4-7.2, 6.0-5.8, 4.8-4.4 and 4.2-3.8. 3. The cytosolic supernatant was also applied to a chromatofocusing column, and again assayed at pH5.5. Four peaks were eluted: minor, but consistent, activity at the beginning of the elution with a pI of near 7.2 or above; a second peak at pH6.0-5.85; a third broad peak with a wide range pH5.3-4.2; and a fourth peak, which was eluted by washing the column with 1m-NaCl, suggesting an isoenzyme with a pI below 4.0 (supported by the result of the isoelectric focusing). 4. If all the chromatofocusing fractions were assayed at pH7.0 or 8.0 (at 1mm-Ca(2+)), only a single sharp peak was detected, with a pI of 4.6-4.8. This peak disappeared on (NH(4))(2)SO(4) fractionation (30-50%) of the cytosolic supernatant, whereas the four peaks with activity at pH5.5 were virtually unaffected. 5. The four activities (assayed at pH5.5) separated by chromatofocusing produced inositol 1:2-cyclic monophosphate, inositol 1-monophosphate and diacylglycerol as enzymic products. 6. We conclude that the Ca(2+)-dependent phosphatidylinositol phosphodiesterase exhibits considerable heterogeneity, both with respect to pH optima of activity, and its isoelectric properties.
 ...
PMID:Heterogeneity of the calcium-dependent phosphatidylinositol phosphodiesterase in rat brain. 629 9

When a membrane preparation, obtained by freezing and thawing nerve endings labeled by preincubation with 32pi, is incubated in the presence of millimolar Ca2+, there is a rapid and selective loss of label from the polyphosphoinositides and a concomitant increase in labeled inositol di- and triphosphates recovered. When the membranes are not prelabeled and are exposed to [gamma-32P]ATP under similar conditions, phosphatidate labeling is enhanced, indicating increased availability of diacylglycerol. These observations provide evidence for the presence of membrane-bound, Ca2+-stimulated phosphodiesterase activity (phospholipase C) acting on endogenous polyphosphoinositides. The implications of these findings are discussed in respect to the "phosphatidylinositol" cycle.
 ...
PMID:Phosphodiesteratic breakdown of endogenous polyphosphoinositides in nerve ending membranes. 630 41

Thyrotropin-releasing hormone (TRH; thyroliberin) stimulated rapid hydrolysis of phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] by a phosphodiesterase (phospholipase C) in GH3 cells, a prolactin-secreting rat pituitary tumour cell line. TRH caused a rapid decrease in the level of PtdIns(4,5)P2 to 60% of control and stimulated a marked transient increase in inositol 1,4,5-trisphosphate, the unique product of phosphodiesteratic hydrolysis of PtdIns(4,5)P2, to a peak of 410% of control at 15 s. TRH also caused decreases in phosphatidylinositol 4-monophosphate (PtdIns4P) and phosphatidylinositol (PtdIns) to 65% and 93% of control at 15 s respectively. Inositol 1,4-bisphosphate was increased to a peak of 450% at 30 s; inositol 1-monophosphate and inositol were not elevated until 30 s and 1 min respectively after TRH addition. To study whether PtdIns(4,5)P2 hydrolysis may be caused by an elevation in cytosolic Ca2+ concentration, the changes induced by TRH in the levels of inositol sugars were compared with the effects of membrane depolarization by high extracellular [K+]. The elevation in cytosolic [Ca2+] induced by K+ depolarization did not change the level of inositol 1,4,5-trisphosphate. These data suggest that phosphodiesteratic hydrolysis of PtdIns(4,5)P2 may be the initial event in TRH stimulation of inositol lipid metabolism in GH3 cells and that PtdIns(4,5)P2 hydrolysis is not stimulated by an elevation in cytosolic Ca2+ concentration. The decreases in PtdIns4P and PtdIns may be due to enhanced conversion of PtdIns into PtdIns4P into PtdIns(4,5)P2 or to their direct hydrolysis by phosphomonoesterases and/or phosphodiesterases. These results are consistent with the hypothesis that TRH-stimulated PtdIns(4,5)P2 breakdown causes Ca2+ mobilization leading to prolactin secretion.
 ...
PMID:Thyroliberin stimulates rapid hydrolysis of phosphatidylinositol 4,5-bisphosphate by a phosphodiesterase in rat mammotropic pituitary cells. Evidence for an early Ca2+-independent action. 631 33

Dispersed mouse pancreas acinar cells were prepared in which phosphatidylinositol had been labeled with myo[2-3H]inositol. During incubation with 0.3 microM cholecystokinin octapeptide (CCK-8) for 15 min, there was a loss of [3H]phosphatidylinositol radioactivity (23%) and a 3-fold gain in trichloroacetic acid-soluble radioactivity. Replacement of NaCl by up to 58 mM LiCl did not significantly affect the amount of CCK-8-stimulated [3H]phosphatidylinositol breakdown or the gain in acid-soluble radioactivity. However, in normal medium, the product of phosphatidylinositol breakdown was almost all inositol, whereas in Li+-containing medium, the product was almost all inositol 1-phosphate. Similar results were obtained with acetylcholine which, in the presence of Li+, gave a dose-responsive increase in inositol 1-phosphate over the concentration range of 0.1 to 10 microM. No increased accumulation of [3H]inositol diphosphate or [3H]inositol triphosphate was detected in stimulated cells. Time courses in the presence of Li+ indicated that the formation of inositol 1-phosphate preceded the formation of inositol. Addition of up to 50 mM myoinositol to the incubation medium showed no diluting effect on the amount of [3H]inositol 1-phosphate found. The accumulation of inositol 1-phosphate is presumably due to the known ability of Li+ to inhibit myoinositol 1-phosphatase. The results provide clear evidence that stimulated phosphatidylinositol breakdown involves a phospholipase C type of phosphodiesterase activity. 1.25 mM Li+ gave half-maximal inositol 1-phosphate accumulation. This is close to the range of plasma Li+ levels which is used therapeutically in psychiatric disorders. In unstimulated cells, [3H]inositol 1-phosphate accumulation in the presence of Li+ corresponded to a breakdown rate for [3H]phosphatidylinositol of 2 to 3%/h.
 ...
PMID:Lithium-induced accumulation of inositol 1-phosphate during cholecystokinin octapeptide- and acetylcholine-stimulated phosphatidylinositol breakdown in dispersed mouse pancreas acinar cells. 632 67

A calmodulin-Ca2+-stimulated cyclic nucleotide phosphodiesterase (EC 3.1.4.17) which hydrolyzed both cGMP and cAMP has been purified about 2000-fold from ovaries of the amphibian Xenopus laevis. Gel filtration through Sephadex G-200 indicated a molecular weight of 140,000. A single, major protein band of molecular weight 66,000 was observed on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In addition to the stimulation by calmodulin-Ca2+, the enzyme was activated 5- to 10-fold by proteolysis and by certain phospholipids. Trypsin activation of the enzyme caused a reduction in the native molecular weight to 90,000 and a loss of the capacity to be stimulated by calmodulin-Ca2+ or by phospholipids. The phosphodiesterase was stimulated by low concentrations (0.1 microgram/ml) of lysophosphatidylcholine and lysophosphatidylethanolamine. This response did not require calcium ions. Phosphatidylinositol, fatty acids, progesterone, and phospholipase C had little or no effect on activity. Simultaneous addition of 1 mM 2-chloro-10-(3-aminopropyl)phenothiazine and lysophosphatidylcholine to the enzyme did not diminish the stimulatory effect of the phospholipid. The activation of the enzyme by all three agents resulted in an increase in the maximum velocity of the reaction without significant modification of the apparent Km values for cGMP (5 microM) or cAMP (30 microM). It was suggested that trypsin removed an inhibitory domain from the enzyme and that calmodulin and phospholipids interact with this same domain, eliminating its capacity to inhibit the active center of the enzyme.
 ...
PMID:Properties of a cyclic nucleotide phosphodiesterase of amphibian oocytes that is activated by calmodulin and calcium, by tryptic proteolysis, and by phospholipids. 632 99

Vasopressin induced a transient increase of 50% in the total concentration of diacylglycerols (determined by g.l.c.) in isolated hepatocytes. The increase was maximal at 0.25 min, and the concentration of diacylglycerols in cells treated with vasopressin had returned to the basal value by 4 min. No change in the concentration of diacylglycerols was observed after the treatment of cells with glucagon. The dependency of this effect on the concentration of vasopressin was similar to that of the effect of the hormone on 45Ca2+ efflux measured at 0.1 mM extracellular Ca2+. Vasopressin increased the proportion of arachidonic acid and stearic acid and decreased the proportion of oleic acid present in the diacylglycerols. In hepatocytes prelabelled with [14C]arachidonic acid, vasopressin increased the amount of [14C]diacylglycerol. The effects of vasopressin on the total concentration of diacylglycerols and [14C]diacylglycerol were mimicked by an exogenous phospholipid phosphodiesterase (phospholipase C) from Clostridium perfringens. The results are consistent with the conclusion that the transient increase in diacylglycerols induced by vasopressin is caused by the rapid hydrolysis of both the phosphoinositides and one or more other phospholipids.
 ...
PMID:A transient increase in diacylglycerols is associated with the action of vasopressin on hepatocytes. 647 30

The fatty acid selectivity of cytosolic phospholipase C (phosphatidylinositol phosphodiesterase) from pig and human platelets towards phosphatidylinositol was evaluated. For this purpose, the relative conversion of rat liver phosphatidylinositol (enriched in stearate and arachidonate) and sheep liver phosphatidylinositol (enriched in stearate plus oleate and containing linoleate and arachidonate) was compared and, in addition, the fatty acid compositions of the diacylglycerol products were determined by gas-liquid chromatography. The cytosolic enzyme exhibited essentially complete specificity for phosphatidylinositol when choline-, ethanolamine-, serine-, or inositol-containing phospholipids labelled with [14C]stearate were tested as substrates. Similar percentage conversions of rat and sheep liver phosphatidylinositols to 1,2-diacylglycerol were found with phospholipase C from either pig or human platelets. Furthermore, the newly formed diacylglycerols and the unreacted phospholipid had fatty acid compositions which were very similar to the corresponding substrates. These results suggest that the phospholipase C from isolated platelet cytosol is highly selective towards phosphatidylinositol, but not with respect to the fatty acid composition of naturally occurring phosphatidylinositol. They also suggest that any preferential release of arachidonoyl diacylglycerol in stimulated human platelets is more likely controlled by compartmentation of the corresponding phosphatidylinositol precursor within platelet membranes and its availability, rather than directly by a marked enzyme preference for arachidonate-containing species.
 ...
PMID:Evaluation of the fatty acid selectivity of a phosphatidylinositol-specific cytosolic phospholipase C from pig and human platelets. 651 12

We examined the degradation of a labeled phosphatidylglycerol (PG) by fibroblasts from a normal control and a patient with Niemann-Pick (NP) disease. The control homogenate had both phospholipase A and phospholipase C activities toward PG, but NP cells had only phospholipase A. The PG phospholipase C of control fibroblasts was solubilized by sonication and freezing and thawing, was most active at pH 5.0, and was inhibited by Ca2-, detergents, sphingomyelin, and 5' AMP. Assay of PG phospholipase C in fibroblast cultures from NP patients with sphingomyelinase deficiency (three designated type A and four type B) confirmed absence of activity, whereas cultures from NP patients without sphingomyelinase deficiency (three designated type C and one with neurovisceral lipidoses and vertical supranuclear ophthalmoplegia) had activities close to those of normal controls. These findings substantiate previous observations of low phosphodiesterase activities in NP disease and suggest that the enzymatic function affected by the NP genes includes specificity toward PG and sphingomyelin. Deficiency of PG phospholipase C may explain the accumulation of bis(monoacylglycero)phosphate in NP disease.
 ...
PMID:Deficiency of phospholipase C acting on phosphatidylglycerol in Niemann-Pick disease. 668 61

Examination of release of labeled glyceride from 2-[1-14C]oleoyl phosphatidylcholine by a soluble extract of human fibroblasts confirmed the presence of phosphodiesterase which is stimulated strongly by sodium taurocholate. This activity was maximal at pH 4.5 and was inhibited by sphingomyelin and 5' AMP. Assay of the phosphatidylcholine phosphodiesterase activity in fibroblast cultures from patients with Niemann-Pick disease revealed a severe deficiency in those cultures also deficient in sphingomyelinase (3 type A and 4 type B) whereas assay of cultures from Niemann-Pick patients without sphingomyelinase deficiency (3 type C and 1 with neurovisceral lipidosis and vertical supranuclear ophthalmoplegia) gave activities similar to controls. The distribution of label in the products of the reactions catalyzed by both control and Niemann-Pick extracts indicates that the phosphodiesterase activity observed was phospholipase C and that phospholipase D was not involved. The close correlation of phosphatidylcholine phospholipase C and sphingomyelinase activities in the control and mutant fibroblasts strongly suggests that both activities are catalyzed by one enzyme. Various alterations in the regulation of the specificity of a multifunctional phospholipase C may underlie phenotypic variation in Niemann-Pick disease.
 ...
PMID:Deficiency of taurocholate-dependent phospholipase C acting on phosphatidylcholine in Niemann-Pick disease. 685 19


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