Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:4.6.1.2 (guanylate cyclase)
 8,497 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The association of [125I-]calmodulin with rat brain synaptosomal plasma membranes, when incubated for 1 h at 25 degrees in the presence or in absence of 20 microM Ca2+, follows a sigmoid path with a Hill coefficient h = 1.79 +/- 0.12 and h = 1.72 +/- 0.11, respectively. The total association of calmodulin with the membrane increased approx. 60%-80% at all the range of calmodulin concentrations used in the presence of 20 microM Ca2+. A three fold increase of guanylate cyclase activity was shown in the presence of low concentrations of calmodulin (up to 10 nM); higher concentrations (up to 40 nM) however, led to a progressive inhibition of the enzyme activity with respect to maximal stimulation. Calmodulin increased the lipid fluidity of synaptosomal plasma membranes labeled with 1,6-diphenyl-1,3,5-hexatriene (DPH), as indicated by the steady-state fluorescence anisotropy [(ro/r)-1]-1. Arrhenius-type plots of [(ro/r)-1]-1 indicated that the lipid separation of the membrane at 22.7 +/- 1.2 degrees was perturbed by calmodulin such that the temperature was reduced to 16.3 +/- 0.9 degrees and 15.5 +/- 0.8 degrees in the absence or in the presence of 20 microM Ca2+. Arrhenius plots of guanylate cyclase and acetylcholinesterase activities exhibited break points at 26.7 +/- 1.4 degrees and 22.3 +/- 1.0 degrees in control synaptosomal plasma membranes, respectively. The break point for the guanylate cyclase was reduced to 16.3 +/- 0.9 degrees in calmodulin treated synaptosomal plasma membranes whereas that of acetylcholinesterase remained unaffected (21.1 +/- 0.9 degrees).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Calmodulin selectively modulates the guanylate cyclase activity by repressing the lipid phase separation temperature in the inner half of the bilayer of rat brain synaptosomal plasma membranes. 256 39

PGE2 and PGA2 incubated for 30 min at 25 degrees C with microsomal membranes isolated from Walker-256 tumour, in the presence of 50 microM indomethacin increase the lipid fluidity estimated by steady-state fluorescence anisotropy [(r0/r)-1]-1, using 1,6-diphenyl-1,3,5-hexatriene (DPH) as probe. The microsomal preparations of Walker-256 tumour contained calcium-stimulated and magnesium-dependent ATPase as well as calmoduling-dependent guanylate cyclese activities. A considerable decrease (approx. 65%) in the activity of the Ca2+-stimulated ATPase was observed when preparations were treated with 10 microM PGE2 and PGA2. A dramatic gradual decrease of the calmodulin-dependent guanylate cyclase activity was also observed at different concentrations of PGE2 and PGA2 (0.25-10 microM). The ATP-dependent uptake of calcium was reduced by approximately 60% in microsomal membranes treated with PGE2 and PGA2. The allosteric properties of Ca2+-stimulated ATPase by Na+, and of guanylate cyclase by Mn.GTP (as reflected by changes in the Hill coefficients, h) were modulated by PGE2 and PGA2. The apparent cooperativity of the Ca2+-ATPase (h + 1.73 +/- 0.21) in control membranes was abolished (h + 1.1 +/- 0.11 and h = 0.9 +/- 0.09) in membranes treated by PGE2 and PGA2 (10 microM), while the allosteric stimulation of guanylate cyclase by Mn.GTP was reduced from h = 2.78 +/- 0.24 in control membranes to h = 1.92 +/- 0.16 and h = 1.73 +/- 0.15 in membranes treated by PGE2 and PGA2 (10 microM), respectively, suggesting that the physical state of Ca2+-stimulated ATPase and guanylate cyclase lipid microenvironments changed from a gel phase to a liquid-crystalline phase. In conclusion, it is suggested that PGE2 and PGA2 promote a phase separation in Walker-256 tumour microsomal membranes. This may be relevant to the Ca2+-calmodulin system and tumour growth inhibition.
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PMID:PGE2 and PGA2 affect the allosteric properties and the activities of calmodulin-dependent guanylate cyclase and Ca2+-stimulated ATPase of Walker-256 tumour microsomal membranes. 256 56

The association of [3H]-Met-enkephalin with synaptosomes isolated from rat brain cortex, when incubated for 30 min at 25 degrees C follows a sigmoid path with a Hill coefficient h = 1.25 +/- 0.04. Binding of Met-enkephalin into synaptosomes was saturable, with an apparent binding constant of 8.33 +/- 0.48 nM. At saturation, Met-enkephalin specific receptors corresponded to 65.5 +/- 7.2 nmol/mg synaptosomal protein. The Hill plot in combination with the biphasic nature of the curve to obtain the equilibrium constant, showed a moderate degree of positive cooperativity in the binding of Met-enkephalin into synaptosomes of at least one class of high affinity specific receptors. Met-enkephalin increased the lipid fluidity of synaptosomal membranes labelled with 1,6-diphenyl-1,3,5-hexatriene (DPH), as indicated by the steady-state fluorescence anisotropy [(ro/r)-1]-1. Arrhenius-type plots of [(ro/r)-1]-1 indicated that the lipid separation of the synaptosomal membranes at 23.4 +/- 1.2 degrees C was perturbed by Met-enkephalin such that the temperature was reduced to 15.8 +/- 0.8 degrees C. Naloxone reversed the fluidizing effect of Met-enkephalin, consistent with the receptor-mediated modulation of membrane fluidity. Naloxone alone had no effect on membrane fluidity. NO release and cGMP production by NO-synthase (NOS) and soluble guanylate cyclase (sGC), both located in the soluble fraction of synaptosomes (synaptosol) were decreased by 82% and 80% respectively, after treatment of synaptosomes with Met-enkephalin (10(-10)-10(-4) M). These effects were reversed by naloxone (10(-4) M) which alone was ineffective in changing NO and cGMP production.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Met-enkephalin receptor-mediated increase of membrane fluidity modulates nitric oxide (NO) and cGMP production in rat brain synaptosomes. 754 Feb 62

Endothelium-derived relaxing factor/nitric oxide (EDRF/NO) is produced by the vascular wall and is a key modulator of vascular tone and blood pressure. Since reduced EDRF/NO release from the endothelium is a major key event in the development of atherosclerosis, we investigated the effect of cholesterol on endothelial cell particulate (membrane-bound) NO synthase activity. Low concentrations (up to 0.2 mM) of liposomal cholesterol progressively activated plasma membrane-bound NO synthase. Increasing cholesterol concentration above that which maximally stimulated enzyme activity produced a progressive inhibition with respect to the control value. In time course experiments using endothelial cell plasma membranes enriched with cholesterol, changes in NO production were followed by analogous changes in soluble guanylate cyclase activity (sGC). N-Monomethyl-L-arginine (L-NMMA) (1 mM) inhibited particulate NO synthase activity at all cholesterol concentrations used with subsequent decreases in cGMP production. Egg lecithin liposomes (free of cholesterol) had no effect on NO synthase activity. A three-fold increase in superoxide (O2-) and a 2.5-fold increase in NO formation followed by an eight-fold increase in peroxynitrite (ONOO-) production by cholesterol-treated microsomes isolated from endothelial cells was observed, one which rose further up to eight-fold in the presence of superoxide dismutase (SOD) (10 U/mL). Cholesterol had no effect on Lubrol-PX solubilized membrane-bound NO synthase or on cytosolic (soluble) NO synthase activities of endothelial cells. Cholesterol modulated lipid fluidity of plasma membranes labelled with 1,6-diphenyl-1,3,5-hexatriene (DPH) as indicated by the steady state fluorescence anisotropy [(ro/r)-1]-1. Arrhenius plots of [(ro/r)-1]-1 indicated that the lipid phase separation of the membranes at 26.2 +/- 1.5 degrees was elevated to 34.4 +/- 1.9 degrees in cholesterol-enriched membranes, consistent with a general decrease in membrane fluidity. Cholesterol-enriched plasma membranes treated with egg lecithin liposomes showed a lipid phase separation at 27.5 +/- 1.6 degrees, indicating the reversible effect of cholesterol on membrane lipid fluidity. Arrhenius plots of NO synthase activity exhibited break point at 26.9 +/- 1.8 degrees which rose to 35.6 +/- 2.1 degrees in 0.5 mM cholesterol-treated plasma membranes and decreased to 21.5 +/- 1.4 degrees in plasma membranes treated with 0.2 mM cholesterol. The allosteric properties of plasma membrane-bound NO synthase inhibited by Mn2+ (as reflected by changes in the Hill coefficient) were changed by cholesterol, consistent with modulations of the fluidity of the lipid microenvironment of the enzyme.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Modulation of particulate nitric oxide synthase activity and peroxynitrite synthesis in cholesterol enriched endothelial cell membranes. 754 Mar 91

Based on our previous findings on the modifying effect of calmodulin (CaM) on the physiochemical properties of biomembrane, we have investigated the possible relationship between intracellular CaM content and endoplasmic reticulum (ER) membrane fluidity and function during liver regeneration. The degree of ER membrane fluidity was estimated by fluorescence polarization analysis with the 1,6-diphenyl-1,3,5-hexatriene probe. Microsomal guanylate cyclase (GC) was used as a functional parameter. The kinetics of the increase in the ER membrane fluidity during liver regeneration was strictly parallel to the CaM surge and was matched by an increase in GC activity. The stimulative effect of splenectomy on liver regeneration and its inhibition by Walker-256 tumor, inferred from the corresponding alterations of CaM levels, were mirrored by the modulation in GC activity. The fluidizing effect of CaM on ER membrane was concluded from the drop in thermotropic transition temperature from 28.3 +/- 1.6 degrees C in control membranes to 17.8 +/- 1.1 degrees C membranes from regenerating livers and to 19.8 +/- 1.2 degrees C in control membranes treated with CaM. Arrhenius plots of GC activity exhibited a transition temperature of 25.5 +/- 1.25 degrees C in controls, which shifted to 20.5 +/- 0.9 degrees C in ER membranes from regenerating livers and to 21.7 +/- 1.1 degrees C in control membranes treated with CaM. The Hill coefficient for the allosteric activation of the GC by Mn.GTP decreased from 1.49 +/- 0.16 in controls to 0.93 +/- 0.085 in membranes from regenerating cells and to 0.86 +/- 0.073 in CaM-treated membranes. Both effects of CaM were consistent with a fluidity increase in the enzyme's lipid microenvironment. The results of the present study suggest that an early key event in liver regeneration may be the CaM-induced modulation of ER membrane fluidity and function.
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PMID:Calmodulin-related changes in microsomal membrane fluidity during liver regeneration. 907 62