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

Adenyl cyclase activity of rat pancreatic islet membrane was increased by secretin, pancreozymin, and isoproterenol, while ACTH, glucagon, growth hormone, and insulin had no effect. Both secretin and isoproterenol activations were enhanced by prostaglandin E1 (PGE1) and GTP. Isoproterenol activation was additive with PGE1, as was that of secretin with PGE1, but only in the presence of GTP. Secretin activation in the presence of PGE1 and GTP was equivalent to NaF stimulation. Kinetic analysis indicated that secretin and GTP increased the maximum velocity of the adenyl cyclase and tended to decrease the apparent affinity of the enzyme for ATP. Glucagon activation of islet membrane adenyl cyclase was dependent upon prior treatment of the membrane preparation with EGTA and the use of inhibitors of proteolytic enzymes during the collagenase digestion phase of islet preparation. These results suggest that hormonal regulation of insulin secretion may be affected by PGE1 and guanine nucleotide modulation of the adenyl cyclase activation process.
...
PMID:Hormonal regulation of pancreatic islet adenyl cyclase. 17 51

A study was made of the effects of various agents on adenylate cyclase in synaptosomes in both the absence and presence of the boiled supernatant from rat cerebral cortex. The activity of adenylate cyclase in these preparations was inhibited by the sulfhydryl reactive agent p-chloromercuribenzoate. Sulfhydryl compounds such cysteine, glutathione and Coenzyme A stimulated the enzymic activity in both the absence and presence of the boiled supernatant. The chelating agent 1.2-bis-(2-dicarboxymethylaminoethoxy)ethane caused a stimulation of the enzymic activity with and without the presence of the boiled supernatant. Adenine nucleotide (adenine, adenosine, AMP and ADP), GTP, Pi and carbamylcholine seemed to have little effect. The stimulatory substance in the boiled supernatant was estimated to have a molecular weight in the range of 1,000-1,300.
...
PMID:Effects of various agents on synaptosomal adenylate cyclase activity in the absence and presence of the boiled supernatant. 18 Mar 22

Liver plasma membranes (LPM) were isolated from rats fed an essential fatty acid-supplemented diet (+EFA) or from rats fed an essential fatty acid-deficient diet (-EFA). The proportions of linoleate and arachidonate in membrane total fatty acids in the -EFA preparations were one-half or less than the values for the +EFA preparations. Basal, F-, or glucagon-stimulated adenylate cyclase activities were significantly lower in EFA-deficient livers than in nondeficient ones. Addition of GTP significantly enhanced glucagon-stimulated adrenylate cyclase in both groups, but extent of stimulation above basal was greater in EFA-deficient livers. Portal vein injection of glucagon in vivo resulted in significantly higher cAMP formation in +EFA livers than in -EFA livers. When glucagon was used in vitro at 1-1,000 nM, stimulation of adenylate cyclase remained lower in EFA-deficient membranes, but extent of stimulation above basal activity was larger in -EFA membranes than in +EFA. Total Na+, K+ (Mg2+)-ATPase from EFA-depleted LPM exhibited significantly higher values of apparent Km and Vmax-5'-Nucleotidase activity, in contrast, was considerably decreased in EFA-deficient rats. These findings show that, in animals, changes in unsaturated fatty acid composition can affect the properties of membrane-bound enzymes. These alterations could be due to changes in membrane physical properties and/or prostaglandin formation.
...
PMID:Effect of essential fatty acid deficiency on activity of liver plasma membrane enzymes in the rat. 18 Mar 55

The prostaglandin endoperoxide prostaglandin H2 (15-hydroxy-9alpha, 11alpha-peroxidoprosta-5,13-dienoic acid) inhibits basal and hormone-stimulated adenylate cyclase in fat cell ghosts. This inhibition by prostaglandin H2 has been found to be antagonized by GTP and Gpp(NH)p. Dose response studies have shown GTP and Gpp(nh)p to be maximally effective at 3.3 muM, the lowest concentration tested. Although the system is exceedingly sensitive to modulation by GTP or Gpp(NH)p UTP, CTP, GMP, and cyclic GMP did not antagonize the antihormone activity of prostaglandin H2. Kinetic studies indicate that the GTP or Gpp(NH)p antagonism of prostaglandin H2 is observable on initial rates of cyclic AMP synthesis, and persists throughout the adenylate cyclase measurements. Preincubation of fat cell ghosts with GTP followed by washing and resuspension results in a prostaglandin H2-sensitive adenylate cyclase system. However, the same preincubation experiment with Gpp(NH)p produces an irreversible antagonism of the prostaglandin H2 inhibition of hormone-stimulated adenylate cyclase. It is suggested that prostaglandin H2 stabilizes the fat cell adenylate cyclase system in a state that is resistant to hormone stimulation, and GTP or Gpp(NH)p overcome this stabilization.
...
PMID:Antagonism of the prostaglandin endoperoxide imhibition of hormone-stimulated adenylate cyclase by guanosine triphosphate and 5'-guanylyl-imidodiphosphate. 18 30

The ability of guanylylimidodiphosphate (GMP=P(NH)P) and guanylylmethylenediphosphonate (GMP-P(CH2)P) to activate adenylate cyclase activity has been studied by incubating these analogs with fat cell membranes followed by thorough washing of the membranes before assay of enzyme activity. GMP-P(NH)P is hydrolyzed by membrane preparations from several tissues. A pyruvate kinase regenerating system maintains the concentration of GMP-P(NH)P and thereby augments the ability of suboptimal concentrations of GMP-P(NH)P to activate adenylate cyclase. GTP inhibits activation of fat cell membrane adenylate cyclase by GMP-P(NH)P but this inhibition is overcome by time. This is consistent with the virtually irreversible nature of the GMP-P(NH)P activation, and with the inability of GTP to reverse the stimulated state of the enzyme. Although the initial rate of enzyme activation is highly dependent on the concentration of GMP-P(NH)P, with increasing times of incubation nearly the same maximal extent of activation is seen over a wide range of concentrations. Thus, it is not possible to estimate true affinity constants (at equilibrium) for GMP-P(NH)P, as anticipated from the virtually irreversible character of the activation process.
...
PMID:Kinetics of irreversible activation of adenylate cyclase of fat cell membranes by phosphonium and phosphoramidate analogs of gtp1. 18 21

(1) The apparent [3H]epinephrine binding parameters of plasma membranes from rat liver and ascites hepatomas such as AH-7974, AH-371A and AH-130, as measured by equilibrium dialysis and/or Millipore filtration, were almost similar to each other. The epinephrine binding sites in the plasma membranes were heterogenous (alpha, beta-receptors and non specific sites), but the pattern of these binding sites in the liver membranes appeared almost similar to that in the hepatoma membranes. 2. The beta-receptor seemed to be specifically involved in the epinephrine-mediated activation of adenylate cyclase of the liver membranes. In spite of the presence of almost similar beta-receptors and adenylate cyclase, the adenylate cyclase of hepatoma membranes was found to be less sensitive to the epinephrine-mediated activation. 3. GTP alone was found to activate adenylate cyclase of liver and hepatoma membranes to some extents when the concentration of ATP was lower (0.3 mM). When GTP was added with epinephrine, a marked, synergistic activation of adenylate cyclase was observed in liver plasma membranes, but not in hepatoma ones. 4. The synergistic activation of adenylate cyclase by epinephrine plus GTP showed a characteristic kinetic feature, reaching a maximal peak within 1 min or so after mixing. 5. Binding of [3H]epinephrine to liver membranes proceeded monophasically in the absence of GTP, while it proceeded biphasically in the presence of GTP, showing the retardation of binding at some earlier stages. GTP added at the time of binding equilibrium induced the temporary release of bound epinephrine from the beta-receptors. The GTP-induced temporary release of bound epinephrine, occurring within 4-5 min after the addition of GTP, was less marked in the hepatoma membranes as compared with the liver membranes. 6. Possible impairment of the GTP-dependent coupling mechanism in the receptor-adenylate cyclase system of hepatoma plasma membranes was suggested.
...
PMID:Comparison of the epinephrine-mediated activation of adenylate cyclase in plasma membranes from liver and ascites hepatomas of rats. 18 40

Determination of specific GTPase (EC 3.6.1.--) activity in turkey erythrocyte membranes was achieved using low concentration of GTP (0.25 muM), inhibition of nonspecific nucleoside triphosphatases by adenosine 5'(beta,gamma-imino-triphosphate (App(NH)p) and suppression of the transfer of gamma-32P from GTP to ADP with an ATP regeneration system. Under these conditions catacholamines caused a 30--70% increase in GTP hydrolysis. The stimulation of GTPase activity by catecholamines required the presence of Mg2+ or Mn2+. DIfferent batches of membranes revealed the following specific activities (pmol 32Pi/mg protein min): basal GTPase (determined in the absence of catecholamine), 6-- 11; catecholamine-stimulated TTPase, 3--7; and residual non-specific NTPase 3--5. The stimulation of GTPase activity by catecholamines fulfilled the stereospecific requirements of the beta-adrenergic receptor, and was inhibited by propranolol. The concentrations of DL-isoproterenol which half-maximally activated the GTPase and adenylate cyclase were 1 and 1.2 muM, respectively. The following findings indicate that the catecholamine-stimulated GTPase is independent of the catalytic production of cyclic AMP by the adenylate cyclase. Addition of cyclic AMP to the GTPase assay did not change the rate of GTP hydrolysis. Furthermore, treatment of the membrane with N-ethylmaleimide (MalNEt) at 0 degrees C which caused 98% inhibition of the adenylate cyclase, had no effect on the catecholamine-stimulated GTPase. The affinity and specificity for GTP in the GTPase reactions are similar to those previously reported for the stimulation of the adenylate cyclase. The apparent Km for GTP in the basal and the catecholamine-stimulated GTPase reaction was 0.1 muM. These GTPase activities were inhibited by ITP but not by CTP and UTP. It is proposed that a catecholamine-stimulated GTPase is a component of the turkey erythrocyte adenylate cyclase system.
...
PMID:Catecholamine-stimulated GTPase activity in turkey erythrocyte membranes. 18 66

The interaction of human chorionic gonadotropin (hCG) with rat adipose tissue was investigated by both metabolic and binding studies. Highly purified preparations of hCG did not affect the adenylate cyclase activity nor the lipolysis of rat adipocytes in the presence or in the absence of GTP. However, it was demonstrated that (a) the hCGs used were biologically active since they stimulated cAMP and testosterone production by rat Leydig cells, and (b) there are receptor sites on the rat ovary that bind [125I]hCG and recognize rat luteinizing hormone (LH). The lack of response cannot then be attributed to a loss of activity of the hormone preparation tested nor to a failure of the rat tissues to recognize an hormone of human origin, but rather to an absence of hCG--LH receptors on the fat cell membrane surface. It is suggested that results previously reported in other laboratories could be explained by the presence of contaminating amounts of lipolytic hormones in their preparations.
...
PMID:The interaction of hCG with rat adipose tissue: apparent lack of hCG--LH receptors. 18 2

Steroidogenesis by Y-1 adrenal tumor cells in culture is stimulated by ATP, adenyl-5'-yl imidodiphosphate (App(NH)), adenosine 5'(beta, alpha-methylene)triphosphate (App(CH2)p), ADP, AMP, NAD, FAD, and adenosine but not by adenine or other nucleoside triphosphates. ATP, App(NH)p, App(CH2)p, and adenosine are active in the micromolar range. Like adrenocorticotropic hormone (ACTH), the onset of stimulation is immediate and occurs to the same extent. Also active are 2'- and 5'-deoxyadenosine and 2-chloroadenosine whereas adenine xyloside, L-riboside, or arabinoside have very low activity. Stimulation is accompanied by rounding of the cells. Dipyridamole, an inhibitor of adenosine transport, increased the response to low concentrations of adenosine, suggesting that adenosine acts externally. Stimulation of steroidogenesis by adenosine or phosphorylated adenosine compounds fails to occur in the presence of crystalline adenosine deaminase, and the effect of the enzyme on adenosine, ATP, or NAD stimulation is reversed by the competitive inhibitor erythro-9-[3-(nonane-2-ol)]adenine. This suggests that the enzyme acts specifically on adenosine and a requirement for the conversion of the above compounds to adenosine seems probable. The inhibition of cAMP effects by adenosine deaminase suggests that some of its effects are also mediated by conversion to adenosine. Similar stimulation is seen in I-10 Leydig tumor cells, but an ACTH-resistant mutant of Y-1 cells, called OS-3, is relatively resistant to adenosine. Adenosine and 2-chloroadenosine stimulate adenylate cyclase in membranes from Y-1 and I-10 cells at concentrations slightly greater than are effective for steroidogenesis. Other nucleosides are ineffective. Like the NH2-terminal 24 residues of adrenocorticotropic hormone (1-24 ACTH), the adenosine effect in Y-1 membranes is rapid and is on the Vmax intercept (versus ATP) and not on the Km. In contrast to steroidogenesis, adenosine is only a partial agonist for adenylate cyclase. It effect occurs in the presence of ITP, GTP, or guanyl-5'-yl imidodiphosphate (Gpp(NH)p). Theophylline inhibits adenosine-stimulated steroidogenesis. Inhibition of adenylate cyclase occurs in the same concentration range but is of the mixed type.
...
PMID:Activation of steroidogenesis and adenylate cyclase by adenosine in adrenal and Leydig tumor cells. 18 24

The lecturer recalls the discovery of glucagon receptors in liver cell membranes, the role of the adenylate cyclase-AMPc system, until recent attempts at purification and isolation of this receptor. He then reviews successively, the problems of estimation, specificity of the interaction, the effects of purine and pyrimidine nucleotides on glucagon receptor interaction, etc. The importance of the two nucleotides GTP and ATP in activation of adenylate cyclase is emphasized. The VIP receptors ("vasoactive intestinal peptide") and secretin receptors are also discussed. In some ways, they resemble glucagon receptors. The possible consequences of these discoveries arethen discussed.
...
PMID:[Glucagon receptors]. 18 43


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---