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:4.6.1.2 (guanylate cyclase)
8,497 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have characterized a magnesium-dependent guanylate cyclase in homogenates of Dictyostelium discoideum cells. 1) The enzyme shows an up to 4-fold higher cGMP synthesis in the presence of GTP analogues with half-maximal activation at about 1 microM guanosine 5'-O-(3-thio)triphosphate (GTP gamma S) or 100 microM guanosine 5'-(beta, gamma-imido)triphosphate; little or no stimulation was observed with GTP, guanosine mono- and diphosphates or with adenine nucleotides, with the exception of the ATP analogue adenosine 5'-(beta, gamma-imido)triphosphate. 2) Both basal and GTP gamma S-stimulated guanylate cyclase activity were rapidly lost from homogenates as was the ability of GTP gamma S to stimulate the enzyme after cell lysis. 3) Inclusion of 25 microM GTP gamma S during cell lysis reduced the KM for GTP from 340 to 85 microM and increased the Vmax from 120 to 255 pmol/min.mg protein, as assayed in homogenates 90 s after cell lysis. 4) Besides acting as an activator, GTP gamma S was also a substrate for the enzyme with a KM = 120 microM and a Vmax = 115 pmol/min.mg protein. 5) GTP gamma S-stimulated, Mg2+-dependent guanylate cyclase was inhibited by submicromolar concentrations of Ca2+ ions, and by inositol 1,4,5-trisphosphate in the absence of Ca2+ chelators. 6) Guanylate cyclase activity was detected in both supernatant and pellet fractions after 1 min centrifugation at 10,000 x g; however, only sedimentable enzyme was stimulated by GTP gamma S. We suggest that the Mg2+-dependent guanylate cyclase identified represents the enzyme that in intact cells is regulated via cell surface receptors, and we propose that guanine nucleotides are allosteric activators of this enzyme and that Ca2+ ions play a role in the maintenance of the enzyme in its basal state.
...
PMID:Regulatory properties of magnesium-dependent guanylate cyclase in Dictyostelium discoideum membranes. 256 93

Dictyostelium discoideum cells have been generated that lack myosin heavy chain (MHC) due to antisense RNA inactivation of the endogenous mRNA or to insertional mutagenesis of the myosin gene. These cells retain chemotactic movement in gradients of the chemoattractant cAMP. Furthermore, cAMP does induce many biochemical and physiological responses in aggregative cells, including binding of cAMP to surface receptors, modification, and down-regulation of the receptor; activation of adenylate and guanylate cyclase, secretion of cAMP; and the association of actin to the Triton-insoluble cytoskeleton. Cells lacking MHC were found to have a requirement for bivalent cations in the medium for optimal chemotaxis and cell aggregation.
...
PMID:Signal transduction, chemotaxis, and cell aggregation in Dictyostelium discoideum cells without myosin heavy chain. 283 47

Transmembrane signal transduction was investigated in four Dictyostelium discoideum mutants that belong to the fgd A complementation group. The results show the following. (a) Cell surface cAMP receptors are present in fgd A mutants, but cAMP does not induce any of the intracellular responses, including the activation of adenylate or guanylate cyclase and chemotaxis. (b) cAMP induces down-regulation and the covalent modification (presumably phosphorylation) of the cAMP receptor. (c) The inhibitory effects of GTP gamma S and GDP beta S on cAMP binding are reduced; the stimulatory effect of cAMP on GTP gamma S binding is lost in fgd A mutants. (d) Basal high-affinity GTPase activity is reduced 40% and the stimulatory effect of cAMP is decreased from 40% in wild type to 30% in fgd A. (e) GTP-mediated stimulation and inhibition of adenylate cyclase is normal in mutant membranes. The results suggest a defective interaction between cell surface cAMP receptors and a specific G-protein in fgd A mutants. This interaction appears to be essential for nearly all signal transduction pathways in Dictyostelium discoideum.
...
PMID:Signal transduction in Dictyostelium fgd A mutants with a defective interaction between surface cAMP receptors and a GTP-binding regulatory protein. 284 45

cAMP induces a transient increase of cAMP and cGMP levels in Dictyostelium discoideum cells. Fast binding experiments reveal three types of cAMP-binding site (S, H and L), which have different off-rates (t0.5, 0.7-15 s) and different affinities (Kd, 15-450 nM). A time- and cAMP-concentration-dependent transition of H- to L-sites occurs during the binding reaction (Van Haastert, P.J.M. and De Wit, R.J.W. (1984) J. Biol. Chem. 13321-13328). Extracellular Ca2+ had multiple effects on cAMP-binding sites. (i) The number of H + L-sites increased 2.5-fold, while the number of S-sites was not strongly affected. (ii) The Kd of the S-sites was reduced from 16 nM to 5 nM (iii) The conversion of H-sites to L-sites was inhibited up to 80%. The kinetics of the cAMP-induced cAMP accumulation was not strongly altered by Ca2+, but the amount of cAMP produced was inhibited up to 80%. The kinetics of the cAMP-induced cGMP accumulation was strongly altered; maximal levels were obtained sooner, and the Ka was reduced from 15 to 3.5 nM cAMP. Ca2+, Mg2+ and Mn2+ increased the number of binding sites, all with EC50 = 0.5 mM. The S-sites and the cGMP response were modified by equal Ca2+ concentrations and by higher concentrations of Mg2+ and Mn2+ (EC50 are respectively 0.4 mM, 2.5 mM and about 25 mM). The conversion of H- to L-sites and the cAMP response were specifically inhibited by Ca2+ with EC50 = 20 microM. It is concluded that cAMP activates guanylate cyclase through the S-sites; adenylate cyclase is activated by the H + L-sites, in which the appearance of the L-sites during the binding reaction represents the coupling of occupied surface cAMP receptors to adenylate cyclase.
...
PMID:cAMP activates adenylate and guanylate cyclase of Dictyostelium discoideum cells by binding to different classes of cell-surface receptors. A study with extracellular Ca2+. 286 84

In Dictyostelium discoideum cells, extracellular cAMP induces the rapid (within 2 s) activation of guanylate cyclase, which is followed by complete desensitization after about 10 s. cAMP binding to these cells is heterogeneous, showing a subclass of fast dissociating sites coupled to adenylate cyclase (A-sites) and a subclass of slowly dissociating sites coupled to guanylate cyclase (B-sites). The kinetics of the B-sites were further investigated on a seconds time scale. Statistical analysis of the association of [3H]cAMP to the B-sites and dissociation of the complex revealed that the receptor can exist in three states which interconvert according to the following scheme. (formula; see text). cAMP binds to the BF-state (off-rate 2.5 s) which rapidly (t1/2 = 3 s) converts to the BS-state (off-rate 15 s) and subsequently (without a detectable delay) into the BSS-state (off-rate 150 s). In membranes, both the BS- and BSS-states are converted to the BF-state by GTP and GDP, suggesting the involvement of a G-protein. Densensitized cells show a 80% reduction of the formation of the BSS-state, but no reduction of the BF- or BS-state. These data are combined into a model in which the transitions of the B-sites are mediated by a G-protein; activation of the G-protein and guanylate cyclase is associated with the transition of the BS- to the BSS-state of the receptor, whereas desensitization is associated with the inhibition of this transition.
...
PMID:G-protein-mediated interconversions of cell-surface cAMP receptors and their involvement in excitation and desensitization of guanylate cyclase in Dictyostelium discoideum. 287 Oct 26

Recently, we demonstrated the presence of multiple folate-binding sites on the cell surface of Dictyostelium discoideum. These sites were divided into two major classes, with different ligand specificities (A and B). Each major class consists of several interconvertible subtypes. In the present report, the ability of 13 folate analogs to activate both adenylate and guanylate cyclase in pre- as well as postaggregative cells is examined. The patterns of correlation between binding and activation data indicate that guanylate cyclase activation is mediated by the B-sites in both developmental stages (P less than 0.001). In postaggregative cells, adenylate cyclase also seems to be activated by the B-sites (P less than 0.001). In contrast, adenylate cyclase activation in preaggregative cells was well correlated with the specificity of A-sites (P less than 0.01). Remarkably, the potencies of activation were less affected by molecular modifications than the binding affinities were, as suggested by a slope of 0.4 in a plot of K0.5 values of activation vs. binding. This observation argues against the existence of a transduction mechanism in which the response is proportional to receptor occupancy. For the B-receptor, however, the degree of receptor occupancy appears to determine the response. The existence of folic acid antagonists is demonstrated, some of which are specific for either A-sites coupled to adenylate cyclase or for B-sites coupled to guanylate cyclase.
...
PMID:Developmental regulation of the pathways of folate-receptor-mediated stimulation of cAMP and cGMP synthesis in Dictyostelium discoideum. 287 51

Adenylate cyclase is the critical enzyme in the chemotactic signal relay mechanism of the slime mold amoeba, Dictyostelium discoideum. However, few studies examining the regulation of this enzyme have been performed in vitro due to the instability of enzyme activity in crude lysates. For studies presented in this communication, a membrane preparation has been isolated that exhibits a high specific activity adenylate cyclase that is stable during storage at -70 degrees C and under assay conditions at 27 degrees C. The enzyme was activated by micromolar concentrations of MnCl2. GTP and its non-hydrolyzable analog, guanosine 5'-(beta, gamma-imino)triphosphate, inhibited the enzyme non-competitively in the presence of either Mg2+ or Mn2+. However, this inhibition was more pronounced in the presence of Mn2+. Since guanylate cyclase activity in the D. discoideum membranes was less than 10% of the adenylate cyclase activity, there could not be a significant contribution by guanylate cyclase toward the production of cyclic AMP. Experiments indicate that D. discoideum adenylate cyclase was also regulated by adenosine analogs. The enzyme was inhibited by 2',5'-dideoxyadenosine and 2'-deoxyadenosine and inhibition was augmented by the presence of Mn2+. However, the inhibition was not entirely consistent with that which would be expected for the P-site of eukaryotic systems because some purine-modified adenosine analogs also inhibited the enzyme. Guanine nucleotides had no effect on the inhibition by either purine-modified or ribose-modified adenosine analogs. The binding of cyclic AMP to its receptor on the D. discoideum membranes was not affected by either MnCl2 or adenosine analogs.
...
PMID:Regulation of Dictyostelium discoideum adenylate cyclase by manganese and adenosine analogs. 288 Jun 7

Dictyostelium discoideum cells contain a single ras gene (Dd-ras) that is highly homologous to mammalian ras genes. Cell transformation with a vector carrying a ras gene with a (glycine----threonine) missense mutation at position 12 causes an altered morphogenesis. Extracellular cAMP signals regulate morphogenesis and induce chemotaxis and the activation and subsequent desensitization of adenylate and guanylate cyclase. cAMP signal transduction was investigated in Dd-ras-transformed cells. Transformants that overexpress the mutated Dd-ras-Thr12 gene show normal activation and desensitization of adenylate cyclase and normal activation of guanylate cyclase. However, cAMP induces a stronger desensitization of guanylate cyclase stimulation in the Dd-ras-Thr12 transformant than in transformants overexpressing the Dd-ras-Gly12 wild-type gene or in untransformed cells. This effect was correlated with a reduced chemotactic sensitivity of the transformant expressing the mutated Dd-ras-Thr12 gene.
...
PMID:Aberrant transmembrane signal transduction in Dictyostelium cells expressing a mutated ras gene. 288 43

Cell fractionation studies have been performed, in order to obtain insight into the subcellular distribution of Dictyostelium adenylate cyclase and guanylate cyclase and also to provide a starting point for further study and isolation of these enzymes and their regulatory components. Adenylate cyclase and cAMP receptors were found in the same membrane fractions, but were distributed different from the plasma membrane marker alkaline phosphatase. Guanylate cyclase was partially soluble, partially particulate. In isopycnic gradients, particulate guanylate cyclase was present in other fractions than cAMP receptors and adenylate cyclase, but in similar ones to alkaline phosphatase. These observations are consistent with the hypothesis that cell-surface cAMP receptors and adenylate cyclase interact via a membrane-bound G-protein, whereas the receptors activate guanylate cyclase via a cytosolic factor. The adenylate cyclase activity in membranes obtained by sucrose gradient centrifugation was retained in the presence of various detergents, while with the same detergents the activity of particulate guanylate cyclase was lost. This adenylate cyclase was solubilized as assessed by gel filtration and centrifugation experiments, and it behaved heterogeneous in fractionation studies. In gel filtration, the major component eluted at a position corresponding to a Stokes radius of 4-7 nm. A purification of about 70-fold as compared to the cell homogenate was obtained by affinity chromatography of adenylate cyclase on ATP-Sepharose. We conclude that cell fractionation provides useful starting material for isolation and further study of Dictyostelium adenylate cyclase.
...
PMID:Cell fractionation, detergent sensitivity and solubilization of Dictyostelium adenylate cyclase and guanylate cyclase. 288 13

Extracellular cAMP induces excitation of adenylate and guanylate cyclase in Dictyostelium discoideum. Continuous stimulation with cAMP leads to adaptation, while cells deadapt upon removal of the cAMP stimulus. Excitation of guanylate cyclase by cAMP has a lag time of approximately 1 s; excitation of adenylate cyclase is much slower with a lag time of 30 s. Excitation of both enzyme activities is less than twofold slower at 0 degrees C than at 20 degrees C. Adaptation of guanylate cyclase is very fast (t1/2 = 2.4 s at 20 degrees C), and virtually absent at 0 degrees C. Adaptation of adenylate cyclase is much slower (t1/2 = 110 s at 20 degrees C) but not very temperature sensitive (t1/2 = 290 s at 0 degrees C). At 20 degrees C, deadaptation of adenylate cyclase is about twofold slower than deadaptation of guanylate cyclase (t1/2 = 190 and 95 s, respectively). Deadaptation of adenylate cyclase is absent at 0 degrees C, while that of guanylate cyclase proceeds slowly (t1/2 = 975 s). The results show that excitation, adaptation, and deadaptation of guanylate cyclase have different kinetics and temperature sensitivities than those of adenylate cyclase, and therefore are probably independent processes.
...
PMID:Differential effects of temperature on cAMP-induced excitation, adaptation, and deadaptation of adenylate and guanylate cyclase in Dictyostelium discoideum. 289 Jun 46


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

---