Showing papers on "Cyclase published in 1981"
TL;DR: F Forskolin would appear to activate adenylate cyclase through a unique mechanism involving both direct activation of the enzyme and facilitation or potentiation of the modulation of enzyme activity by receptors or the guanyl nucleotide-binding subunit, or both.
Abstract: The diterpene, forskolin [half-maximal effective concentration (EC50), 5-10 microM] activates adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] in rat cerebral cortical membranes in a rapid and reversible manner. Activation is not dependent on exogenous guanyl nucleotides and is not inhibited by guanosine 5'-O-(2-thiodiphosphate) when assayed with adenosine 5'-[beta, gamma-imido]triphosphate as substrate. GTP and GDP potentiate responses to forskolin. The activations of adenylate cyclase by forskolin and guanosine 5'-[beta, gamma-imido]triphosphate p[NH]ppG are not additive, whereas activations by forskolin and fluoride are additive or partially additive. The responses of adenylate cyclase to forskolin or fluoride are not inhibited by manganese ions, whereas the response to p[NH]ppG is completely blocked. Activation of adenylate cyclase by forskolin is considerably greater than the activation by fluoride in membranes from rat cerebellum, striatum, heart, and liver, while being about equal or less than the activation by fluoride in other tissues. Forskolin (EC50, 25 microM) causes a rapid and readily reversible 35-fold elevation of cyclic AMP in rat cerebral cortical slices that is not blocked by a variety of neurotransmitter antagonists. Low concentrations of forskolin (1 microM) augment the response of cyclic AMP-generating systems in brain slices to norepinephrine, isoproterenol, histamine, adenosine, prostaglandin E2, and vasoactive intestinal peptide. Forskolin would appear to activate adenylate cyclase through a unique mechanism involving both direct activation of the enzyme and facilitation or potentiation of the modulation of enzyme activity by receptors or the guanyl nucleotide-binding subunit, or both.
1,600 citations
TL;DR: Forskolin, a novel diterpene activator of adenylate cyclase in membranes and intact cells, activates the enzyme in membranes from mutant cyc-S49 murine lymphoma cells and the soluble enzyme from rat testes.
712 citations
Journal Article•
TL;DR: Forskolin, a diterpene of the labdane family, activates adenylate cyclase in broken cell preparations as well as in intact tissues and provides an invaluable tool for the investigation of the role of cyclic AMP in physiological responses to hormones.
Abstract: Forskolin, a diterpene of the labdane family, activates adenylate cyclase in broken cell preparations as well as in intact tissues. This activation does not require the guanine nucleotide regulatory subunit of the enzyme and probably occurs via an interaction with the catalytic subunit of adenylate cyclase. Activation of adenylate cyclase by forskolin results in marked increases in levels of intracellular cyclic AMP in a variety of eukaryotic cells. Low concentrations of forskolin which alone elicit small increases in intracellular cyclic AMP greatly potentiate hormonal activation of adenylate cyclase in a number of intact cells. Forskolin elicits cellular responses which have been proposed to be dependent o cyclic AMP as a second messenger. Forskolin, thus provides an invaluable tool for the investigation of the role of cyclic AMP in physiological responses to hormones, both through it direct activation of adenylate cyclase and through its ability to potentiate hormonal activation of adenylate cyclase.
580 citations
TL;DR: Fractions that are enriched in the 52,000-dalton protein reconstitute hormone-stimulated adenylate cyclase activity more efficiently and are activated by GTP analogs more rapidly than are fractions that are essentially free of this polypeptide.
464 citations
TL;DR: It is concluded that IAP may exert its unique influence on the heart cell membrane causing profound modification of the coupling mechanism involved in the receptor-mediated activation or inhibition of adenylate cyclase.
323 citations
TL;DR: The focus of the present review is on the regulatory effects of guanine nucleotides and on the growing body of evidence suggesting that the guanin nucleotide regulatory protein (G-protein) may represent the functional communicator between hormone-occupied receptors and the adenylate cyclase enzyme.
Abstract: Since the discovery that cyclic AMP mediates the action of a large number and variety of hormones (Sutherland & Robison, 1966), there has been considerable interest in trying to understand the molecular mechanisms by which hormone occupancy of specific cell surface receptors results in activation of membrane-bound adenylate cyclase, the enzyme responsible for synthesis of cyclic AMP from ATP. Although the earliest concepts of the adenylate cyclase system suggested that hormones might regulate adenylate cyclase activity via binding at allosteric sites on the catalytic moiety, more recently it has been demonstrated that adenylate cyclase systems consist of separable receptor and catalytic subunits (Orly & Schramm, 1976; Limbird & Lefkowitz, 1977; Haga et al., 1977a) and, in addition, a third separable component which confers the multiple regulatory effects of guanine nucleotides on the adenylate cyclase system (for a review focusing on the biochemical properties of the separate components see Ross & Gilman, 1980). The focus of the present review is on these regulatory effects of guanine nucleotides and on the growing body of evidence suggesting that the guanine nucleotide regulatory protein (G-protein) may represent the functional communicator between hormone-occupied receptors and the adenylate cyclase enzyme. The perspective of this review is a historical one; it attempts to summarize the critical observations that established the important role of guanine nucleotides in regulating adenylate cyclase activity and to describe how the further exploration
303 citations
TL;DR: A mechanism whereby membrane receptors are linked to adenylate cyclase appears to be modified by exposure of islet cells to IAP, suggesting that neither the catalytic nor the GTP-regulatory component of the membrane adanylatecyclase complex is the site of IAP action.
247 citations
TL;DR: In this paper, it was shown that progesterone selectively inhibited membrane-bound adenylate cyclase activity, after addition to intact oocytes or in cell-free experiments; this specificity confirms the proposed membrane site of action for the hormone when reinitiating meiosis.
Abstract: Recent experimental evidence indicates that progesterone acts at the cell surface to trigger protein synthesis and to reinitiate the first meiotic division in Xenopus laevis oocytes1,2. The steroid hormone is physiologically released by follicle cells surrounding oocytes in the ovaries, and this naturally occurring event can be reproduced in vitro by adding progesterone to the incubation medium. Recently, cyclic AMP has been implicated in the mechanism of progesterone action in oocytes3,4; there was an almost immediate decrease in cyclic AMP concentration in oocytes after addition of progesterone in vitro, whether or not the oocytes were pretreated with cholera toxin5,6. Adenylate cyclase in X. laevis oocytes is compartmentalized, >50% soluble and ∼30% is found in the plasma membrane-containing fraction7. We report here that physiological concentrations of progesterone selectively inhibit membrane-bound adenylate cyclase activity, after addition to intact oocytes or in cell-free experiments; this specificity confirms the proposed membrane site of action for the hormone when reinitiating meiosis and is the first example of a ‘direct’ enzymatic action of a steroid (not by protein synthesis) related to a physiological function.
212 citations
TL;DR: It is concluded that receptor-mediated stimulation of GTP hydrolysis is the mechanism by which opiates and other inhibitory hormones lower adenylate cyclase activity in NG108-15 cell membranes.
Abstract: Specific, GTP hydrolysis catalyzed by membranes prepared from neuroblastoma--glioma (NG108-15) hybrid cells can be measured in the presence of adenosine-5'-[beta, gamma-imido] triphosphate (p[NH]ppA), ATP, and a nucleotide triphosphate-regenerating system. Opiates and opioid peptides stimulate low Km GTP hydrolysis when measured in the presence of Na+ and Mg2+. Opiate stimulation is rapid, stereospecific, and reserved by the antagonist naloxone. Potencies of opiates as stimulators of GTP hydrolysis and as inhibitors of adenylate cyclase are closely correlated. Agents that stimulate adenylate cyclase, including prostaglandin E1, 2-Cl-adenosine, secretin, and NaF, have little or no effect upon the rate of GTP hydrolysis. Opiates have no effect upon either adenylate cyclase or GTPase activity in membranes prepared from C6-BU1 glioma cells, which lack opiate receptors. In view of the pivotal role of GTP in the activation of adenylate cyclase, we conclude that receptor-mediated stimulation of GTP hydrolysis is the mechanism by which opiates and other inhibitory hormones lower adenylate cyclase activity in NG108-15 cell membranes.
209 citations
204 citations
TL;DR: This chapter highlights physiological and metabolic effects on enzyme activities of vanadium, affecting the transition state of phosphate, which seems to have an affinity for the binding sites on these enzymes.
Abstract: Publisher Summary This chapter highlights physiological and metabolic effects on enzyme activities. Vanadium, a group V element, belongs to the first transition series and can form compounds mainly in valence states 3+, 4+, and 5+, both anionic and cationic species. Several criteria of essentiality of an element are satisfied by the properties of vanadium such as low molecular weight, excellent catalytic activity, appropriate atomic structure, its position as a transition metal, ability to form chelates potentially with biologically active compounds, ubiquity in the geosphere and possibly in the biosphere, homeostatic regulation by controlled accumulation and rapid excretion, deficiency in animals and plants showing characteristic symptoms, and low toxicity on oral intake. At least three significant enzymes of the plasma membrane are affected by vanadate—Na, K-ATPase is inhibited in nanomolar concentrations and adenylate cyclase and NADH oxidase are activated in micro-molar to milli-molar concentrations. These enzymes are interrelated. ATP is the substrate for the first two, and both substrates are nucleotides. Vanadate, affecting the transition state of phosphate, seems to have an affinity for the binding sites on these enzymes.
TL;DR: It was determined that enkephalin inhibition was dependent on GTP and there were differences in the potencies of various opiate peptides in their inhibition of striatal adenylate cyclase activity, with Met5‐ > Leu5‐enke phalin > β‐endorphin.
Abstract: The conditions in which Leu(5)-enkephalin inhibition of striatal adenylate cyclase was observed were defined. It was determined that enkephalin inhibition was dependent on GTP. The apparent K(m) for GTP in opiate inhibition was determined to be 0.5 and 2 micrometer when 0.1 mM- and 0.5 mM-ATP were used as substrate. ITP, but not CTP or UTP, could substitute for GTP in the reaction. Though the addition of monovalent cations-Na+, K+, Li+, Cs+, and choline+--stimulated striatal adenylate cyclase activity, enkephalin inhibition of striatal adenylate cyclase did not require Na+ when theophylline was used as the phosphodiesterase inhibitor. Under optimal conditions, i.e., 20 micrometer-GTP and 100 mM-Na+, Leu(5)-enkephalin inhibited the strial adenylate cyclase activity by 23-27%. When the enkephalin regulation of the cyclase activity was further characterized, it was observed that Leu(5)-enkephalin inhibited the rate of the enzymatic reaction. Kinetic analysis revealed that the opioid peptide decreases V (max) values but not the K(m) values for the substrates Mg2+ and Mg-ATP. Agents such as MnCl(2), NaF, and guanyl-5'-ylimido-diphosphate, which directly activated the adenylate cyclase, antagonized the opiate inhibition. Levorphanol and (-)naloxone were more potent than dextrorphan and (+) naloxone in inhibiting adenylate cyclase and in reversing the enkephalin inhibition, respectively. There were differences in the potencies of various opiate peptides in their inhibition of striatal adenylate cyclase activity, with Met5- > Leu(5)-enkephalin > beta-endorphin. The opiate receptor through which the enkephalin inhibition was observed is most likely delta in nature, since in the presence of either Na+ or K+, the magnitude of the alkaloid inhibition was reduced, whereas the peptide inhibition was either potentiated or not affected.
TL;DR: Dopamine‐stimulated adenylate cyclase activity was potently antagonised by various neuroleptic drugs including fluphenazine, α‐flupenthixol and α‐piflutixol, and to a lesser extent by the butyrophenone derivatives haloperidol and spiperone.
Abstract: A specific dopamine-sensitive adenylate cyclase has been identified in homogenates of the teleost (carp) retina. Maximal stimulation by 100 microM-dopamine resulted in a 5--10-fold increase in adenylate cyclase activity with half-maximal stimulation occurring at a concentration of 1 microM. l-Noradrenaline and l-adrenaline were some 10 times less potent than dopamine whilst the alpha- and beta-adrenoreceptor agonists, l-phenylephrine and dl-isoprenaline were inactive. Apomorphine elicited a partial stimulation of adenylate cyclase activity whilst various ergot alkaloids produced mixed agonist/antagonist responses. Dopamine-stimulated adenylate cyclase activity was potently antagonised by various neuroleptic drugs including fluphenazine, alpha-flupenthixol and alpha-piflutixol, and to a lesser extent by the butyrophenone derivatives haloperidol and spiperone. The benzamide derivatives, metoclopramide and sulpiride, together with the alpha- and beta-adrenoreceptor blocking agents, phentolamine and propranolol respectively were essentially inactive at blocking dopamine-stimulated adenylate cyclase activity. These data suggest the presence of a highly specific dopamine-sensitive adenylate cyclase in homogenates of teleost retina possessing similar pharmacological properties to the dopamine-sensitive adenylate cyclase observed in the mammalian central nervous system.
TL;DR: It is shown here that colchicine, vinblastine and cis- unsaturated fatty acids enhance G unit-mediated activation of adenylate cyclase, implying that microtubules or tubulin are involved in the attachment of the G unit to the membrane.
Abstract: The adenylate cyclase system, which mediates cellular responses to a variety of hormones and neurotransmitters, contains at least three plasma membrane-associated proteins: the hormone receptor, the regulatory or guanyl nucleotide-binding unit (G unit) and the catalytic moiety. Activation of the enzyme after binding of hormone to the receptor involves binding of GTP to the G unit1. Activation can be enhanced by increasing the fluidity of the membrane with unsaturated fatty acids2 with the local anaesthetic prilocaine3, and perhaps, in vivo, by phospholipid methylation4. Disruption of microtubules increases localized mobility of membrane proteins in a manner similar to that of unsaturated fatty acids5 and can enhance cyclic AMP accumulation in intact leukocytes6–9. We therefore decided to investigate whether there is a direct interaction between micro-tubules and adenylate cyclase. We show here that colchicine, vinblastine and cis- unsaturated fatty acids enhance G unit-mediated activation of adenylate cyclase, implying that microtubules or tubulin are involved in the attachment of the G unit to the membrane.
TL;DR: Strittmatter et al. as mentioned in this paper showed that calmodulin interacts with the adenylate cyclase catalytic unit but does not seem to affect the function of the G/F unit.
Journal Article•
TL;DR: It is suggested that lymphocytes possess functional receptors for VIP and that this peptide may play a role in modulation of lymphocyte function.
Abstract: Vasoactive intestinal polypeptide (VIP) was found to be a potent stimulator of lymphocyte adenylate cyclase activity. VIP-induced activation of adenylate cyclase was specific for lymphocytes among peripheral blood cells; i.e., VIP did not stimulate the adenylate cyclase activity of neutrophils, monocytes, or platelets. The VIP-induced activation of lymphocyte adenylate cyclase was time, temperature, and concentration dependent. VIP and the GTP analog, Gpp(NH)p, acted synergistically to stimulate lymphocyte adenylate cyclase; stimulation by VIP and PGE1 was additive; and VIP activation was antagonized by somatostatin. VIP-mediated activation of lymphocyte adenylate cyclase was observed in normal human T cells, B cells obtained from a patient with chronic lymphocytic leukemia, and a human T cell culture line. The Raji human B cell culture line did possess adenylate cyclase activity, but this activity was not stimulated by VIP. These results suggest that lymphocytes possess functional receptors for VIP and that this peptide may play a role in modulation of lymphocyte function.
TL;DR: There is a postsynaptic dopamine receptor on carp horizontal cells that is associated with adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1].
Abstract: Horizontal cells of the carp retina were separated from other retinal cell types by using enzymatic dissociation and velocity sedimentation at unit gravity. Fractions containing horizontal cells were tested for their ability to accumulate cyclic AMP in the presence of various putative neurotransmitters. Micromolar concentrations of dopamine, when added in the presence of 3-isobutyl-1-methylxanthine, stimulated cyclic AMP accumulation in these isolated cells. The dopamine-dependent accumulation of cyclic AMP in intact isolated horizontal cells was blocked by nanomolar concentrations of dopamine antagonists such as haloperidol, (+)-butaclamol, and fluphenazine. The results indicate that there is a postsynaptic dopamine receptor on carp horizontal cells that is associated with adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1].
TL;DR: The regulatory component (G/F) of adenylate cyclase has been purified from turkey erythrocyte plasma membranes by adaptation of procedures developed for purification of the rabbit liver protein by inclusion of high concentrations of NaCl to facilitate extraction and reconstitution of the protein.
Journal Article•
TL;DR: There is good evidence that hormone-dependent adenylate cyclase is involved in the cell mechanisms through which many hormones regulate tubular functions, and the nature of the hormonal effect induced via cAMP is not yet established.
Abstract: In addition to the well established action of PTH in proximal tubules and of AVP in collecting tubules, polypeptide hormones were recently shown to regulate transport properties in other tubular portions. Although still scarce, such physiological studies using isolated perfused tubules demonstrated hormonal effects in those nephron segments observed to contain responsive adenylate cyclase and not in the others. Moreover, the same effects were elicited by applying exogenous cAMP or cAMP derivatives. There is, therefore, good evidence that hormone-dependent adenylate cyclase is involved in the cell mechanisms through which many hormones regulate tubular functions. The effects obtained varied depending on the segment of tubule used. It is not yet established whether the nature of the hormonal effect induced via cAMP is entirely specified by the responding cell types or is also specified by the hormone itself. Further studies are needed to clarify this important problem, as well as many other as yet unsolved questions. There is obviously much more to learn about the hormonal regulation of tubular cell functions by using appropriate biochemical and physiological micromethods.
TL;DR: The activation of adenylate cyclase by vasoactive intestinal peptide was used as a model to investigate the molecular mechanisms triggered by the occupancy of dopamine recognition sites in rat anterior pituitary, and it is inferred that stimulation of D-2 (dopamine) receptors may affect pituitaries secretion by inhibiting the activation of anterior pituitsary adenYLatecyclase by VIP or other secretagogues.
Abstract: The activation of adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] by vasoactive intestinal peptide (VIP) was used as a model to investigate the molecular mechanisms triggered by the occupancy of dopamine recognition sites in rat anterior pituitary. Dopamine failed to change the basal enzyme activity, but it inhibited the stimulation of adenylate cyclase elicited by VIP. Apomorphine, 2-amino-6,7-dihydroxy-1,2,3,4-tetrahydronaphthalene, and 2-bromo-alpha-ergocryptine mimicked the effect of dopamine, whereas (-)-sulpiride and and classical neuroleptics antagonized it. Dopamine failed to modulate the activation of pituitary adenylate cyclase by prostaglandin E1, which does not increase prolactin secretion. From these results we infer that stimulation of D-2 (dopamine) receptors may affect pituitary secretion by inhibiting the activation of anterior pituitary adenylate cyclase by VIP or other secretagogues.
TL;DR: It is concluded that 5‐HT acts on two separate receptors, a 5‐ HT1 receptor acting through calcium and a 5-HT2 receptor which mediates its effects through cyclic AMP.
Abstract: 1 5'-Hydroxytryptamine (5-HT) stimulates the formation of two separate second messengers in the salivary gland of the blowfly. Activation of adenylate cyclase raises adenosine 3',5'-monophosphate (cyclic AMP) whereas the hydrolysis of phosphatidylinositol (PI) is associated with an increase in calcium permeability. The possibility that these two signal pathways might be controlled by separate 5-HT receptors was studied by testing the specificity of 5-HT analogues and antagonists. 2 The parent compound 5-HT was found to stimulate both cyclic AMP formation and the related parameters of PI hydrolysis and calcium transport with similar dose-response relationships. 3 Certain analogues such as 4- and 5-fluoro-alpha-methyltryptamine were capable of raising cyclic AMP levels and stimulating fluid secretion but did not stimulate the hydrolysis of PI or the entry of calcium. 4 Other analogues, which had chloro or methyl substituents at the 5-position, were found to stimulate the hydrolysis of PI and the transport of calcium at much lower doses than those required to stimulate the formation of cyclic AMP. 5 Antagonists were also found to exert selective effects. Methysergide was a potent inhibitor of PI hydrolysis whereas cinanserin was far more selective in blocking the stimulatory effect of 5-HT on cyclic AMP formation. 6 It is concluded that 5-HT acts on two separate receptors, a 5-HT1 receptor acting through calcium and a 5-HT2 receptor which mediates its effects through cyclic AMP.
Journal Article•
TL;DR: The results show that pharmacologically relevant concentrations of ethanol can alter adenylate cyclase activity and was found to be reversible and was not blocked by the dopaminergic antagonist butaclamol, the alpha adrenergic antagonist phentolamine or the beta adrenergic antagonists propranolol.
Abstract: The effects of ethanol on adenylate cyclase activity were investigated in homogenates of mouse striatum. Ethanol (34--340 mM) elicited a linear increase in basal and dopamine-stimulated adenylate cyclase activities. The increase in dopamine-stimulated activity was statistically significant at ethanol concentrations of 68 mM and above. The increase in maximal adenylate cyclase activity observed in the presence of ethanol was not entirely due to the increase in basal activity. In the presence of 100 and 300 mM ethanol maximal adenylate cyclase activities were increased by 26 and 71% even after correcting for the increase in basal activity. The concentration of dopamine required for half-maximal activation was not changed by the presence of ethanol. Activation of adenylate cyclase by ethanol was found to be reversible and was not blocked by the dopaminergic antagonist butaclamol, the alpha adrenergic antagonist phentolamine or the beta adrenergic antagonist propranolol. Concentrations of ethanol of up to 500 mM did not change either the affinity of the receptor for [3H]-spiroperidol or the density of binding sites. A decrease in the affinity of the receptor for the radioligand was observed at higher concentrations of ethanol. The affinity of the receptor for dopamine was decreased by 2-fold in the presence of 300 mM ethanol. Addition of 300 microM GTP elicited a 5-fold decrease in the affinity o the receptor for dopamine in both the presence and absence of ethanol. The activation of adenylate cyclase by ethanol was not unique to striatal tissue. In studies carried out with homogenates of cerebral cortex and cerebellum, addition of ethanol increased basal, isoproterenol-stimulated and sodium fluoride-stimulated activities. The results show that pharmacologically relevant concentrations of ethanol can alter adenylate cyclase activity.
Journal Article•
TL;DR: Calmodulin is important both for the sensitivity of striatal adenylate cyclase to dopamine and the maximal velocity of the reaction, which suggests that, in the presence of physiological concentrations of calcium, dopamine stimulation would be curtailed unless calmodulin were present.
Abstract: The effect of an endogenous calcium-binding protein, calmodulin, on basal and dopamine-stimulated adenylate cyclase activity in rat striatum was studied. Basal adenylate cyclase activity in a rat striatal particulate preparation depleted of calmodulin was stimulated by calmodulin as well as the guanyl nucleotides, guanosine triphosphate and guanyl-59-yl-imidodiphosphate. The presence of guanyl nucleotides was required for dopamine stimulation of adenylate cyclase activity in the membrane preparation. Calcium inhibited dopamine-stimulated adenylate cyclase activity, decreasing the maximal velocity by 50%. When calmodulin was added to the assay with calcium, the V max was restored to that found in the absence of calcium and the K act for dopamine was further decreased more than 2-fold. The effects of calmodulin on basal and dopamine-sensitive adenylate cyclase activity were specific for calmodulin, since these effects were not obtained in the presence of troponin C, a calcium-binding protein from muscle. This work demonstrates that calmodulin is important both for the sensitivity of striatal adenylate cyclase to dopamine and the maximal velocity of the reaction. Furthermore, this work suggests that, in the presence of physiological concentrations of calcium, dopamine stimulation would be curtailed unless calmodulin were present.
TL;DR: Evidence of 3′: 5′-cyclic nucleotide phosphodiesterases in higher plants, together with adenylate cyclase, a specific cyclic AMP binding protein, and calmodulin means that plants possess all the necessary components for a functional cyclicAMP-regulated system.
Journal Article•
TL;DR: Data are presented that Li, too, markedly reduces activity of beta-adrenergic adenylate cyclase in humans, and the effect is specific, since the plasma cyclic AMP response to glucagon is not inhibited.
TL;DR: The growth in vitro of human breast cancer cells, line MCF-7, was inhibited by a daily supplement of L-arginine and it is suggested that arginine may play a specific role in this process.
Abstract: The growth in vitro of human breast cancer cells, line MCF-7, was inhibited by a daily supplement of L-arginine (1 milligram per milliliter). Arginine acted synergistically with dibutyryl adenosine 3',5'-monophosphate (cyclic AMP) (10(-6) molar) to enhance the growth inhibitory effect: the cell replication ceased completely within 2 days after treatment. The growth arrest accompanied a change in cell morphology and was preceded by increases in the cellular concentration of cyclic AMP, adenylate cyclase, and type II cyclic AMP-dependent protein kinase activities as well as a decrease of estrogen binding activity. The results suggest that growth of human breast cancer cells is subject to cyclic AMP-mediated regulation and that arginine may play a specific role in this process.
TL;DR: In membrane preparations ofhuman platelets, whose adenylate cyclase is inhibited by a-adrenergic agonists in a GTP-dependent manner, the influence of epinephrine on GTPase activity is studied and it is reported here that epinphrine inhibits adenolatecyclase and stimulates a low Km GTP enzyme via cy-adRenoceptors in this system.
TL;DR: One mechanism by which cortisone modulates beta-adrenergic receptor function appears to be through facilitating the formation of the high affinity state of the receptor, resulting in greater coupling of receptor occupation with adenylate cyclase activation.
Abstract: β-Adrenergic agonists form high affinity complexes with receptors, resulting in activation of the associated adenylate cyclase. To examine the formation of the high affinity state of the receptor, curves were constructed for the competition of the full β-adrenergic agonist isoproterenol, partial agonists cobefrin and soterenol, and the antagonist propranolol for [3H]dihydroalprenolol binding to β-adrenergic receptors on human neutrophil membranes. Curve modeling by computer yielded a two-state binding model for the agonists, with distinct dissociation constants for the high (KH) and low (KL) affinity states. The ratio of dissociation constants (KL/KH) was found to be well correlated (P < 0.01) with the drug’s intrinsic activity for stimulation of adenylate cyclase. Thus, the degree of coupling of receptor occupation with adenylate cyclase activation is correlated with the magnitude of KL/KH. Administration of cortisone to humans resulted in a substantial rise in the proportion of receptors in the high aff...