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

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Query: EC:4.6.1.1 (adenylate cyclase)
19,190 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The present studies examine the initial events in the action of PTH, namely receptor binding and adenylate cyclase activation in the postobstructed canine kidney. Both kidneys were removed from five mongrel dogs 2 h after relief of unilateral ureteral obstruction (UUO) of 42 h duration. Basolateral membranes (BLM) were prepared from both the UUO and contralateral (control) kidneys. Maximal activation of adenylate cyclase by PTH was 35% lower (P less than 0.01) in BLM from UUO than control kidneys (3869 +/- 200 vs. 5978 +/- 425 pmol cAMP/mg protein X 30 min). The concentration of PTH required for half-maximal activation of the enzyme was unchanged. Addition of 1 mM GTP failed to correct the decreased enzyme activity in response to PTH of BLM from kidneys with UUO. NaF activation, a measure of interaction of the nucleotide regulatory component (G/F) with the catalytic unit of the adenylate cyclase was similar in BLM from UUO and control kidneys. Similarly, activation of the catalytic unit of the enzyme by Mn2+ was not different. Specific binding of [125I]Nle8, Nle8, Tyr34-bovine PTH NH2 was markedly reduced (P less than 0.01) in BLM from UUO vs. control (6.37 +/- 1.20 vs. 2.43 +/- 0.09 fmole bound/microgram protein). There was no change in hormone affinity for the binding site. These data indicate that there is decreased activation of adenylate cyclase by PTH as a consequence of apparent loss of receptors for the hormone in the BLMs of renal tubular cells of postobstructed kidneys. These abnormalities may play a role in the abnormal regulation of phosphorus excretion after ureteral obstruction.
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PMID:Impaired parathyroid hormone receptor-adenylate cyclase system in the postobstructed canine kidney. 298 70

Rat reticulocytes contain a cytosol activator protein (RCAP) that augments catecholamine-sensitive adenylate cyclase activity in reticulocyte membranes. A highly purified preparation of RCAP, obtained by Sephacryl S-200 chromatography, was used to elucidate further its mechanism of action. The specific activity of the S-200 fraction to augment isoproterenol responsiveness was increased approximately 1,100-fold over the starting material, from 1.2 to 1,300 nmol cAMP formed per mg RCAP. The mol wt of RCAP is approximately 20,000. The effect of RCAP to enhance isoproterenol responsiveness was apparent within 20 sec, virtually abolishing the normal lag time of hormone-activated adenylate cyclase. In addition to its effects on catecholamine-responsive adenylate cyclase, RCAP significantly increased basal [21 +/- 3 (+/- SEM) to 41 +/- 4 pmol/mg protein X 30 min; P less than 0.02], guanyl-5'-yl-imidodiphosphate-associated (3173 +/- 213 to 4339 +/- 365 pmol/mg X 30 min; P less than 0.03), and fluoride-associated (5152 +/- 64 to 5807 +/- 58 pmol/mg X 30 min; P less than 0.05) adenylate cyclase activities. RCAP also altered the characteristics of agonist binding to the beta-adrenergic receptor of reticulocyte membranes, causing an increase in the apparent IC50 for isoproterenol from 0.7 +/- 0.2 to 7.9 +/- 1.6 microM (P less than 0.001). Similar to its effects on reticulocytes, RCAP enhanced isoproterenol- and prostaglandin E2-sensitive adenylate cyclase activity in the wild-type S49 lymphoma cell and shifted the binding isotherm for isoproterenol rightward. In cyc-, the mutant that lacks the stimulatory guanine nucleotide-binding protein (Ns) and in UNC, the mutant in which receptors are uncoupled from N, RCAP was ineffective. Moreover, RCAP decreased agonist affinity for the beta-adrenergic receptor in wild-type S49 cells, but not in cyc- or UNC cells. These observations suggest that RCAP requires a functional Ns unit for its effects on hormone-sensitive adenylate cyclase activity.
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PMID:Cytosol activator protein from rat reticulocytes requires the stimulatory guanine nucleotide-binding protein for its actions on adenylate cyclase. 298 18

The activity of adenylate cyclase was examined in corpora lutea (CL) obtained from rhesus monkeys at specific stages in the luteal phase of the menstrual cycle [3-5, 6-8, 9-12, 13-15, and 16 days (menses) after the midcycle LH surge]. The conversion of [alpha-32P]ATP to [32P]cAMP was used to monitor adenylate cyclase activity. cAMP production in luteal homogenates was assessed in the absence (basal activity) and presence of maximum stimulatory doses of forskolin (100 microM), 5'-guanylylimidodiphosphate [GMP-P(NH)P; 50 microM], GTP (50 microM), and GTP plus increasing doses of hLH and hCG. Basal activity was low in the early luteal phase (days 3-5; mean +/- SE, 1.2 +/- 0.2 pmol cAMP/mg protein X min), increased (P less than 0.05) by the midluteal phase (days 6-8 and 9-12, 2.1 +/- 0.4 and 2.0 +/- 0.3 pmol/mg X min, respectively), and then declined (P less than 0.05) during the late luteal phase (days 13-15 and 16-menses, 1.6 +/- 0.3 and 1.2 +/- 0.5 pmol/mg X min, respectively). Activity stimulated by GTP and GMP-P(NH)P [e.g. GMP-P(NH)P approximately 12 times basal level] followed the same pattern as basal activity during the luteal phase. In contrast, cAMP production in the presence of forskolin did not change significantly throughout the luteal phase. In the midluteal phase (days 6-8 and 9-12; n = 12), hCG and human LH (hLH) stimulated adenylate cyclase in a similar dose-dependent manner. Maximal stimulation of cAMP production by hCG was about 10% greater (P less than 0.05) than that by hLH; the activation constant was 12.3 nM for hCG and 28.3 nM for hLH. The maximal response to hLH and hCG as well as the sensitivity of adenylate cyclase to activation by hLH were greater (P less than 0.05) in the midluteal phase than in the early or late luteal phase. Decreased basal, gonadotropin-stimulated, and guanine nucleotide-stimulated cAMP production and diminished sensitivity of adenylate cyclase to hLH correlated with a decline (P less than 0.05) in circulating progesterone and luteal weight during the late luteal phase. Thus, the adenylate cyclase system of the rhesus monkey CL undergoes significant changes during the luteal phase which are associated with the development and regression of the CL of the menstrual cycle. Mechanisms that modulate gonadotropin and nucleotide activation of adenylate cyclase without interfering directly with the catalytic unit are implicated in the changes that accompany luteolysis.
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PMID:Adenylate cyclase in the corpus luteum of the rhesus monkey. III. Changes in basal and gonadotropin-sensitive activities during the luteal phase of the menstrual cycle. 299 15

It is known that the secretion of PTH is often impaired in association with aluminum (Al3+) accumulation in patients with renal failure. The mechanisms involved remain ill defined. Since adenylate cyclase plays a role in the regulation of PTH secretion, these studies examine the effects of Al3+ on parathyroid adenylate cyclase. In membranes from normal bovine parathyroid glands, basal adenylate cyclase activity, in the presence of 0.2 mM ATP and 20 mM Mg2+, increased by 22% as Al3+ was raised from 0-10 microM. Higher Al3+ concentrations caused a progressive decrease in adenylate cyclase activity, reaching 68% inhibition of control activity at 2 mM Al3+. Since adenylate cyclase activation is influenced by the interaction of multiple sites within the adenylate cyclase complex, the nature of the inhibition by Al3+ was explored by examining the interaction of Al3+ with substrate ATP and with Mg2+, an allosteric activating metal ion. In the presence of 20 mM Mg2+, Al3+ concentrations of 1-2 mM resulted in noncompetitive inhibition with respect to ATP [decrease in maximum velocity (Vmax) from 4176 in the absence of Al3+ to 1106 pmol cAMP/mg protein X 15 min; Michaelis Menten constant (Km) for ATP was unchanged]. In contrast, at fixed ATP (0.2 mM), 0.5 mM resulted in competitive inhibition of adenylate cyclase with respect to Mg2+, whereas at higher Al3+ concentrations the inhibition was noncompetitive. When Mg2+ was replaced by Mn2+ (enzyme activity reflects the activity of the catalytic unit), the inhibitory effect of Al3+ on adenylate cyclase activity was abolished. These data suggest that the inhibition of parathyroid adenylate cyclase by Al3+ occurs at the level of the allosteric metal activating site. These data provide a potential mechanism for the inhibition of PTH secretion by Al3+.
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PMID:Effects of aluminum on bovine parathyroid adenylate cyclase. 402 88

The mechanisms involved in the renal resistance to the phosphaturic action of PTH during dietary phosphorus deprivation remain ill defined. Previous studies in dogs from our laboratory demonstrated that baseline excretion of cAMP and the increment after administration of parathyroid extract were markedly reduced during dietary phosphorus deprivation. The present studies examine the initial events in the actions of PTH, namely receptor binding and adenylate cyclase activation, in renal cortical membranes from normal and phosphorus-deprived animals. Mongrel dogs were fed a diet deficient in phosphorus for 4-6 weeks. Plasma phosphorus fell from 4.2 +/- 0.4 to 1.4 +/- 0.3 mg/dl. In renal cortical membranes from these animals, basal adenylate cyclase activity was not different from that in control normal animals. However, PTH-stimulated enzyme activity was markedly reduced (5785 +/- 303 pmol cAMP/mg protein X 30 min in controls vs. 2612 +/- 406 pmol cAMP/mg protein X 30 min; P less than 0.01). Kact (PTH concentration for half-maximal enzyme activation) was unchanged. PTH receptor binding assessed with [Nle8,Nle18,Tyr34]bovine PTH-(1-34) NH2 was not different in the two groups. The decreased PTH-stimulated adenylate cyclase activity was not corrected by GTP. Activation of adenylate cyclase by NaF was reduced in membranes from the phosphorus-deprived animals, whereas enzyme activation by guanylylimidodiphosphate was similar in both groups. Enzyme activity in the presence of Mn++ was not different from the control value. These data indicate that during dietary phosphorus deprivation there is uncoupling of the PTH receptor-adenylate system of canine kidney. This abnormality may play a role in the renal resistance to PTH during dietary phosphorus deprivation.
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PMID:Uncoupling of the parathyroid hormone receptor-adenylate cyclase system of canine kidney during dietary phosphorus deprivation. 608 72

In the present study we have investigated the conditions for optimal adenylate cyclase (AC) activity in preparations of human myocardial biopsies, with emphasis on both basal enzyme activity and isoproterenol response. Different preparation procedures (homogenates, membrane particles) of the same biopsy showed no difference in relative response to isoproterenol, although absolute activities, using protein concentration for normalization, showed some variance. The AC-receptor complexes of the preparations were also stable when stored on ice for 3 h, and both basal and stimulated AC activities were constant at a wide range of protein concentrations (2.9-31.9 micrograms/tube), and throughout 92 min incubation. The effects of varying Mg2+, guanyl nucleotides (GTP, GMP-P(NH)P), and ATP concentrations on myocardial AC activities were also investigated under both basal conditions as well as after isoproterenol stimulation. The apparent Km for the substrate (Mg X ATP) binding to the AC was approximately 0.1 mmol/l. Isoproterenol stimulated the AC activity by increasing Vmax (41 to 142 pmol/mg protein X min) without any change in the apparent Km. Maximal relative activation by isoproterenol was achieved at pH 6.5-7.0. The concentration of isoproterenol causing half maximal AC stimulation was approximately 0.1 micrograms/ml (2 X 10(-4) mmol/l). Half maximal inhibition of isoproterenol (4 micrograms/ml) stimulated AC activity was obtained by 0.025 micrograms/ml propranolol (8 X 10(-5) mmol/l). The sensitivity and precision of this assay should make it possible to measure AC activity as well as isoproterenol response in very small quantities of myocardial tissue. This could provide a method for studying receptor functions of sick hearts by endomyocardial biopsies.
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PMID:Catecholamine responsive adenylate cyclase in human myocardial preparations. Properties and optimalization of assay conditions. 608 39

The effects of the adenylate cyclase agonists cholera toxin and prostaglandin E2 on carbonic anhydrase activity in vitro was measured in choroid plexuses isolated from Sprague-Dawley rats. Choroid plexuses were incubated in buffer at 38 degrees C (pH 7.4) with either cholera toxin or prostaglandin E2 (PGE2) at a concentration and for a time period that had been shown in earlier studies to result in maximal stimulation of cyclic AMP production. Cholera toxin (10 micrograms/ml) caused a twofold increase (p < .001) in choroid plexus carbonic anhydrase activity when cholera toxin treated plexuses [20.92 +/- .46 mol CO2/(min)(mg protein X 10(-8)] were compared with plexuses exposed to heat inactivated cholera toxin (10.92 +/- .43). When choroid plexuses were homogenized and separated into a 10,000 g pellet and a supernatant fraction, the supernatant carbonic anhydrase was unresponsive to cholera toxin stimulation. In the pellet fraction, which contained all the cellular adenylate cyclase, challenge with cholera toxin produced a significant increase in carbonic anhydrase activity (p < .01). Control activity was 10.9 +/- 1.2 mol CO2/(min)(mg protein X 10(-8), while carbonic anhydrase activity in fractions exposed to cholera toxin was 28.4 +/- 0.8. PGE2 had no effect, however, upon choroid plexus carbonic anhydrase activity. Since both PGE2 and cholera toxin stimulate cyclic AMP production in vitro, a compartmental model of secretory control is proposed.
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PMID:The effect of cholera toxin on choroid plexus carbonic anhydrase activity in vitro. 610 78

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