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Cyclase

About: Cyclase is a research topic. Over the lifetime, 10162 publications have been published within this topic receiving 388566 citations.


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Journal ArticleDOI
TL;DR: In this paper, the 5′-N-ethylcarboxamido[3H]adenosine (NECA) was found to have a rapid, reversible and dependent on protein concentration, pH and temperature.
Abstract: Adenosine receptors in human platelet membranes have been characterized by radioligand binding and measurement of adenylate cyclase activity. Binding of 5′-N-ethylcarboxamido[3H]adenosine ([3H]NECA) was rapid, reversible and dependent on protein concentration, pH and temperature. Due to a rapid rate of dissociation (t1/2 approximately 20 s) binding was highest at 0° C. Adenosine deaminase and GTP alone did not influence [3H]NECA binding, whereas several divalent cations decreased binding. Saturation experiments revealed two different binding sites for [3H]NECA, with Kd values of 0.16 and 2.9 μmol/l and Bmax values of 8.4 and 33.4 pmol/mg of protein. In competition experiments NECA was the most potent adenosine agonist (IC50 0.5 μmol/l), followed by 2-chloroadenosine (IC50 6.3 μmol/l) and adenosine (IC50 12μmol/l). A similar rank order of potencies was observed for the stimulatory effect of adenosine analogues on platelet adenylate cyclase. NECA stimulated adenylate cyclase activity with an EC50 value of 0.5 μmol/l and was approximately 4-fold more potent than (−)N6-phenylisopropyladenosine [(−)PIA]. However, (−)PIA and N6-cyclohexyladenosine did not significantly affect [3H]NECA binding, an observation not consistent with the stimulatory effect on adenylate cyclase. The adenosine antagonists 3-isobutyl-1-methylxanthine, theophylline and caffeine showed IC50 values between 98 and 5,600 μmol/l. [3H]PIA bound to platelet membranes with very low affinity and was not displaced by NECA. The [3H]NECA binding to human platelet membranes satisfies essential criteria for Ra adenosine receptors and, with some limitations, should be of value for the characterization of adenosine receptors in Ra subtype selective cells.

102 citations

Journal ArticleDOI
TL;DR: It is suggested that dex increases (-)ISO stimulation of adenylate cyclase in ROS 17/2.8 cells by jointly increasing the number of hormone receptors and the abundance of Gs, the guanine nucleotide binding regulatory protein.
Abstract: Treatment of ROS 17/2.8 cells with dexamethasone (dex) increases (-)isoproterenol (ISO)-, PTH-, cholera toxin-, guanine nucleotide-, NaF-, and forskolin-stimulated adenylate cyclase activity. Enhanced hormone stimulation was first apparent 12 h after dex addition. (-)-[3H]Dihydroalprenolol binding, displaceable by ISO, increased up to 2-fold in dex-treated cells. This effect depended on protein synthesis and closely paralleled the extent and time course of the increase in adenylate cyclase stimulation. In dex-treated cells there was also an increase in the maximum velocity of guanyl-5'-yl imidodiphosphate-stimulated adenylate cyclase, a decrease in the lag time for guanyl-5'-yl imidodiphosphate enzyme activation in the presence of ISO from 3 to 1 min, increased stimulation of adenylate cyclase by cholera toxin, and increased labeling of 47,000 and 42,000 mol wt proteins by [32P]NAD in the presence of cholera toxin. [32P]NAD ribosylation in the presence of pertussis toxin resulted in the labeling of 40,000 mol wt protein, which was also increased by 20-50% in dex-treated cells. However, pertussis toxin treatment did not augment or reduce the effect on hormone stimulation, although it increased the cAMP response to PTH and (-)ISO. These findings suggest that dex increases (-)ISO stimulation of adenylate cyclase in ROS 17/2.8 cells by jointly increasing the number of hormone receptors and the abundance of Gs, the guanine nucleotide binding regulatory protein.

102 citations

Journal ArticleDOI
TL;DR: The ability of angiotensin II to inhibit cyclic AMP synthesis may provide an explanation for the observed effects of guanine nucleotides on 125I-angiotens in II binding to plasma membranes.

102 citations

Journal ArticleDOI
TL;DR: Ulastructural examination of rat caudate-putamen demonstrates that the immunoreactivity for the components of the cyclic GMP system is predominantly distributed within the medium-spiny neuron subtype of this structure.

102 citations

Journal ArticleDOI
TL;DR: The results indicate that NCB-20 cells possess at least two species of serotonin receptors, which independently regulate cellular functions, and activation of adenylate cyclase does not directly affect membrane potential or acetylcholine release, and serotonin-dependent cell depolarization does not affect cyclic AMP or cyclic GMP synthesis in the cell lines tested.
Abstract: Serotonin activates adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] of NCB-20 neuroblastoma--brain hybrid cells with an activation constant of 530 nM, but has little or no effect on cellular cyclic AMP or cyclic GMP content of NIE-115 neuroblastoma or NG108-15 hybrid cells. In homogenates of NCB-20 hybrid cells, lysergic acid diethylamide stimulates adenylate cyclase activity (Kact = 12 nM) and partially inhibits (Ki = 10 nM) the stimulation of adenylate cyclase activity by serotonin. No desensitization was detected of serotonin receptors coupled to adenylate cyclase. Serotonin also depolarizes NCB-20, NG108-15, and NIE-115 cells and increases acetylcholine release. Serotonin receptors mediating depolarizing responses desensitize rapidly and reversibly, and the depolarizing effects of serotonin are neither mimicked nor inhibited by lysergic acid diethylamide. These results indicate that (i) NCB-20 cells possess at least two species of serotonin receptors, which independently regulate cellular functions, (ii) activation of adenylate cyclase does not directly affect membrane potential or acetylcholine release, and (iii) serotonin-dependent cell depolarization does not affect cyclic AMP or cyclic GMP synthesis in the cell lines tested.

102 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202324
202257
202145
202048
201939
201856