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)

Inhibitors of pancreatic islet lipoxygenase (LPX) impair nutrient-induced insulin (I) release. To define the mechanism of action of these inhibitors, studies were carried out at subthreshold glucose concentrations (0-1.7 mM) in order to minimize any effects of LPX blockade on the potentiating effect of extracellular fuels. Barium chloride (Ba2+; 2 mM) increased 45Ca2+ release from prelabeled islets in Ca2+-free medium and, thus, is a model for the mobilization of intracellular Ca2+ stores. Inhibition of LPX (using nordihydroguaiaretic acid, BW755c [3-amino-1-(trifluomethyl-phenyl)2-pyrazoline] or butylated hydroxytoluene) did not have any consistent effect on the influx of Ba2+ (as assessed by 133Ba uptake) or on the consequent release of cellular Ca2+ stores; however, each LPX inhibitor vitiated Ba2+-induced I release. The LPX inhibitors were not merely acting as nonspecific antioxidants, since two inhibitors which do not act by scavenging hydroperoxides (5,8,11,14-eicosatetraynoic acid and 15-hydroxy-5,8,11,13-eicosatetraenoic acid) also impeded the effect of Ba2+ on I secretion; furthermore, a series of hydroxyl radical scavengers, reducing agents, or agents that block nonenzymatic and/or NADPH-activated lipid peroxidation did not inhibit I secretion. LPX inhibitors also blocked the residual I response to 16.7 mM glucose in Ca2+-free medium. Additionally, they reduced secretion induced by 46 mM K+ or 1 mM isobutylmethylxanthine (provided in the presence of extracellular Ca2+), without inhibiting K+- or isobutylmethylxanthine-induced Ca2+ fluxes. Stimuli sensitive to LPX blockade were also antagonized by antimycin A (an inhibitor of energy flux) or TMB-8 [8-(N,N-diethylamino)octyl 3,4,5-trimethoxybenzoate hydrochloride; which appeared to deplete critical intracellular Ca2+ stores]. In contrast, the effects of exogenous phospholipase C (and several other Ca2+-dependent membrane-active agonists) were resistant to the LPX inhibitors, TMB-8, and antimycin A; thus, LPX inhibitors are not nonspecific global poisons of all Ca2+-dependent exocytotic hormone release. We conclude that LPX (or a very similar enzyme) may modulate the effects (or redistribution) of an ATP-dependent trigger pool of Ca2+ at a site distal to and independent of its mobilization by primary islet agonists. LPX inhibitors also blocked secretion induced by 12-O-tetradecanoyl-phorbol-13-acetate; this effect may reflect an effect of LPX on the activation of protein kinase C or a modulation of its synergism with the same trigger Ca2+ pool(s).
...
PMID:Lipoxygenase inhibitors reduce insulin secretion without impairing calcium mobilization. 310 21

We have investigated the role of protein kinase C (PKC) in LHRH-induced LH and FSH secretion and LHRH priming. Hemipituitary glands from prooestrous rats were incubated with agents known to affect PKC and with or without LHRH, during which time the secretion of gonadotrophins was measured. Phorbol esters and phospholipase C, activators of PKC, released LH and FSH in a concentration-dependent manner and potentiated the LHRH-induced secretion of gonadotrophins in parallel with their ability to release these hormones alone. Inhibitors of PKC had either no effect on LH release (1-(5-isoquinolinesulphonyl)-2-methylpiperazine hydrochloride) or they augmented LHRH-induced gonadotrophin release (polymyxin B and 8-(N,N-diethylamino) octyl-3,4,5-trimethoxybenzoate). Neither the activators nor the inhibitors of PKC, when present with LHRH, caused any change in LHRH priming, even though the activators alone produced a release of gonadotrophins that showed a temporal pattern similar to that produced by LHRH priming. The profiles of effects on LH and FSH secretion were always qualitatively similar. These results show that PKC may be involved in general regulation of gonadotrophin release but that it is not important in acute responses to LHRH nor in LHRH self-priming.
...
PMID:The role of protein kinase C in LHRH-induced LH and FSH release and LHRH self-priming in rat anterior pituitary glands in vitro. 312 15

Phospholipase A has been solubilized from the sarcoplasmic reticulum of rat heart by treatment with Tris buffer, potassium chloride, taurodeoxycholate or octyl glucoside. On HPLC gel permeation, two phospholipases were identified at the void volume of a TSK 3000 column and at an apparent molecular mass of 60 kDa. The two activity peaks exhibited a predominance of phospholipase A1 activity (83-91%) and a lesser phospholipase C activity (4-9%) using sonicated 1-palmitoyl-2[1-14C]oleoylphosphatidylcholine liposomes as substrate. The voiding phospholipase A peak, which represented the bulk of the recovered activity, exhibited a requirement for calcium ions in the 0.3-3 microM range. The heat stability and response to mercuric ions was studied and some similarities were noted between the solubilized sarcoplasmic reticulum phospholipases A and the cytosolic phospholipases A of rat heart. It is speculated that the cytosolic phospholipase A which we reported earlier may represent in part phospholipase A released from sarcoplasmic reticulum during isolation of the subcellular membrane fractions.
...
PMID:Solubilization and partial characterization of phospholipase A from rat heart sarcoplasmic reticulum. 316 81

The mode of membrane anchorage of three kidney microvillar membrane ectoenzymes has been examined. The release of aminopeptidase P (EC 3.4.11.9) from kidney membranes by bacterial phosphatidylinositol-specific phospholipase C (PI-PLC) and the pattern of detergent solubilization of this ectoenzyme implies that it is anchored to the membrane via a covalently attached glycosyl-phosphatidylinositol moiety. As deduced by phase separation in Triton X-114, octyl-glucoside solubilized the amphipathic form of aminopeptidase P, whereas the PI-PLC-released form displayed hydrophilic properties. In contrast, the pattern of detergent solubilization of two microvillar carboxypeptidases and their resistance to release from the membrane by bacterial PI-PLC suggest that these two ectoenzymes are not anchored via phosphatidylinositol.
...
PMID:Ectoenzymes of the kidney microvillar membrane. Aminopeptidase P is anchored by a glycosyl-phosphatidylinositol moiety. 327 35

Recent evidence has shown that the outer, overt, malonyl-CoA-inhibitable carnitine palmitoyltransferase (CPTo) activity resides in the mitochondrial outer membrane [Murthy & Pande (1987) Proc. Natl. Acad. Sci. U.S.A. 84, 378-382]. A comparison of CPTo activity of rat liver mitochondria with the inner, initially latent, carnitine palmitoyltransferase (CPTi) of the mitochondrial inner membrane has revealed that the presence of digitonin and several other detergents inactivates CPTo activity. The CPTi activity, in contrast, was markedly stimulated by various detergents and phospholipid liposomes. These findings explain why in previous studies, which used digitonin or other detergents to expose, separate and purify the CPT activities, the inferences were drawn that (a) the ratio of latent to overt CPT was quite high, (b) both the CPT activities could be ascribed to one active protein recovered, and (c) the observed lack of malonyl-CoA inhibition indicated possible loss/separation of a putative malonyl-CoA-inhibition-conferring protein. Although both CPTo and CPTi were found to catalyse the forward and the backward reactions, CPTo showed greater capacity for the forward reaction and CPTi for the backward reaction. The easily solubilizable CPT, released on sonication of mitoplasts or of intact mitochondria under hypo-osmotic conditions, resembled CPTi in its properties. When octyl glucoside was used under appropriate conditions, 40-50% of the CPTo of outer membranes became solubilized, but it showed limited stability and decreased malonyl-CoA sensitivity. Malonyl-CoA-inhibitability of CPTo was decreased also on exposure of outer membranes to phospholipase C. When outer membranes that had been exposed to octyl glucoside or to phospholipase C were subjected to a reconstitution procedure using asolectin liposomes, the malonyl-CoA-inhibitability of CPTo was restored. A role of phospholipids in the malonyl-CoA sensitivity of CPTo is thus indicated.
...
PMID:Some differences in the properties of carnitine palmitoyltransferase activities of the mitochondrial outer and inner membranes. 343 81

Tissue-specific (intestinal) and tissue-nonspecific (kidney) rat alkaline phosphatases are released from their respective brush border membranes by different enzymes. To elucidate the mechanism underlying their membrane attachment, we tested the ability of these enzymes to partition into lipid or aqueous phases both before and after treatment with phospholipases and proteases. Interaction with Triton X-114 micelles was eliminated or decreased by treatment of intestinal enzyme with phospholipase A2 or papain, while only phosphatidylinositol (PI)-specific phospholipase C (PIPLC) and subtilisin were effective with the kidney enzyme. Binding to octyl Sepharose for the intestinal enzyme was decreased by phospholipase A2 more than by PIPLC, whereas the reverse was true for the kidney enzyme. Treatment with phospholipases decreased the apparent mass of the phosphatases by 50-80 kDa, presumably due to loss of bound lipid and detergent. PIPLC treatment of the kidney, but not the intestinal enzyme, prevented binding of the phosphatase to phospholipid vesicles. These results show that both enzymes are bound to respective membranes by hydrophobic anchor peptides to which phospholipids are bound. However, their sensitivity to phospholipases is different. The data are consistent with the hypothesis that, in the kidney enzyme, the PI is bound covalently, while with the intestinal enzyme, binding of PI appears to be tight but not covalent.
...
PMID:Hydrophobic interactions of brush border alkaline phosphatases: the role of phosphatidyl inositol. 381 62

Intercellular gap-junctional communication was measured using [14C]citrulline incorporation in co-cultures of argininosuccinate lyase-deficient human fibroblasts and argininosuccinate synthetase-deficient Chinese Hamster V79 cells. As previously shown, in this system junctional communication is completely inhibited by the tumor promoting phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA). In the absence of extracellular calcium, TPA inhibition was less pronounced. However, synergism with calcium ionophore A23187 could not be demonstrated. Chlorpromazine, trifluoperazine and 3,4,5-trimethoxybenzoic acid 8-(diethylamino)octyl ester partially antagonised the effect of TPA. No antagonism was demonstrable between calmidazolium and TPA. Treatment of co-cultures with exogenous phospholipase C or 1-oleoyl-2-acetylglycerol (OAG) resulted in communication inhibition, suggesting that protein kinase C activation is involved in the mechanism of phorbol ester-mediated communication inhibition. However co-cultures which had been made refractory to TPA by prolonged exposure to high concentrations remained sensitive to inhibition by phospholipase C and OAG. These results suggest either that diacylglycerol can produce other effects independent of protein kinase C activation, or that refractoriness to phorbol esters is not simply due to a decrease in the amount of protein kinase C.
...
PMID:Studies on the mechanism of phorbol ester-induced inhibition of intercellular junctional communication. 392 85

Through hydrophobic interaction, sphingomyelin was adsorbed to agarose beads containing octyl groups by a stepwise dilution procedure. This immobilized lipid was used as a substrate for three bacterial phospholipases C (E.C. 3.1.4.3.). The degradation with time of this substrate showed two different fractions of the substrate according to hydrolysing velocity in the early part of the time-curve when phospholipases C from Bacillus cereus and Clostridium perfringens were used. The early fractions could be predigested by the enzymes, a procedure which resulted in linear time-curves. The corresponding early part of the time-curve for phospholipase C from Staphylococcus aureus was linear, indicating a comparatively large early fraction of the substrate for this enzyme. The stock gel of the immobilized lipid substrate could be stored for months. It was easily and reproducibly handled as a water suspension. After enzymatic hydrolysis the substrate was rapidly separated from enzyme and product by filtration. The enzyme assay presented thus represents a convenient way to avoid the difficulties connected with the use of temporary sonicated suspensions as substrate for bacterial phospholipases C.
...
PMID:Enzymatic hydrolysis of immobilized sphingomyelin by three bacterial phospholipases C. 627 45

Recently we described a saturable, high-affinity binding site for vesicular stomatitis virus (VSV) on the surface of Vero cells that appears to mediate viral infectivity. To isolate this binding site, we have extracted Vero cells with the detergent, octyl-beta-D-glucopyranoside. The dialyzed detergent extract specifically inhibits the saturable, high-affinity binding of 35S-methionine-labeled VSV to Vero cells. The inhibitory activity is resistant to protease, neuraminidase and heating to 100 degrees C. It is soluble in chloroform-methanol and inactivated by phospholipase C, suggesting that it is a phospholipid. Of various purified lipids tested, only phosphatidylserine was capable of totally inhibiting the high-affinity binding of VSV. The half-maximal inhibitory concentration for phosphatidylserine was 1 microM. Phosphatidylserine also inhibited VSV plaque formation by 80%-90%; Herpes simplex virus plaque formation was unaffected. Centrifugation and electron microscopy studies have shown that phosphatidylserine-containing liposomes bind to VSV. The finding that phosphatidylserine directly binds to VSV and inhibits VSV attachment and infectivity suggests that plasma membrane phosphatidylserine could function as a binding site or portion of a binding site for VSV.
...
PMID:Inhibition of VSV binding and infectivity by phosphatidylserine: is phosphatidylserine a VSV-binding site? 629 4

In human neutrophils, alkaline phosphatase (AlkPase), a low-affinity receptor for IgG (FcRIIIB), and complement decay accelerating factor (DAF) are glycosyl-phosphatidylinositol (GPI)-anchored proteins. Varying greatly in biological function these three integral membrane proteins exhibit regulated cell surface expression in neutrophils. Defined by their common membrane-linkage motif, AlkPase, FcRIIIB, and DAF can be released from the lipid bilayer by the action of phosphatidylinositol-specific phospholipase C and are relatively resistant to low temperature extraction with Triton X-100 (TX-100). In this study we show that neutrophil AlkPase, FcRIII, and DAF display differential extractibility; they are relatively insensitive to TX-100 solubilization at 4 degrees C, but are readily extracted with TX-100 at 37 degrees C or by the detergent octyl glucoside at 4 degrees C. The differential extractibility of these GPI-anchored proteins is the same in unstimulated cells, where these proteins exist primarily in an intracellular pool, and stimulated cells, where they are expressed principally at the cell surface. However, no differential extraction effect is observed with two neutrophil transmembrane proteins, complement receptor 1 (CD35, CR1) and MHC Class I in either stimulated or unstimulated cells.
...
PMID:Solubilization of glycosyl-phosphatidylinositol-anchored proteins in quiescent and stimulated neutrophils. 753 73


<< Previous 1 2 3 4 5 6 Next >>

---