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At least 19 recordsLinked to original sources

PubMed1976

Cyclic AMP and growth of Ehrlich ascites tumor cells. Lack of cyclic AMP elevation in nutritionally deprived cells and mechanism of retardation of growth by dibutryl cyclic AMP.

Cyclic AMP levels in Ehrlich ascites tumor cells changed little after deprivation of cells of essential nutrients, serum, glucose and amino acids, deprival of each of which leads to marked inhibition of growth and protein synthesis. Cyclic AMP levels also changed little after the addition of these nutrients to deprived cells. Thus cyclic AMP is not likely to be the intracellular mediator for growth regulation by these three nutrients. Elevation of cyclic AMP levels for short periods by exposure of cells to choleratoxin or theophylline produced only slight changes in parameters of protein synthesis (polyribosome pattern and rate of [3H]leucine incorporation). An exposure for 1 day to dibutyryl cyclic AMP did not inhibit cell growth. However, prolonged exposure to dibutyryl cyclic AMP inhibited the multiplication of Ehrlich ascites cells both in suspension and in stationary cultures. No morphological effects were evident in the former; in the latter, cells attached firmly to the substratum and formed elongated cytoplasmic processes. Inhibition of cell multiplication by dibutyryl cyclic AMP was related to cell density and to serum concentration. Cells in dibutyryl cyclic AMP-containing media plated at low cell densities multiplied as rapidly as control cells. The final densities cells reached were determined by the serum concentration; in dibutyryl cyclic AMP-containing media these densities were about one-half those of respective control cells. Limitation of cell multiplication by dibutyryl cyclic AMP was reversed by the addition of serum, by resuspending cells at lower densities, or by resuspending cells in media without dibutyryl cyclic AMP. These findings suggested that dibutyryl cyclic AMP may affect the utilization of serum factors by cells. Dibutyryl cyclic AMP did not inactivate serum factors and did not change the rate at which cells depleted the growth medium of serum factors. Dibutyryl cyclic AMP may limit cell multiplication by increasing the cellular requirement for serum factors.

Amino Acids↗

PubMed1977

The cyclic AMP response to glucagon. Comparison of tissue and plasma cyclic AMP levels in the rabbit.

The effects of glucagon on tissue and plasma cyclic AMP levels have been investigated in rabbits anesthetized with urethane. Glucagon (2 nmole/kg.) caused at least a twofold increase in hepatic cyclic AMP, which reached a peak within two minutes and declined to basal values after 40 minutes. Plasma cyclic AMP also increased at least twofold, reaching a peak at 10 minutes and declining to basal values after 60 minutes. Glucagon (20 nmole/kg.) stimulated hepatic and plasma cyclic AMP in a manner indistinguishable from that observed at the lower dose. Hepatectomy abolished the plasma cyclic AMP responses to glucagon, and no significant stimulation of cyclic AMP concentration was noted in the heart, adipose tissue, small bowel, or kidney. Cyclic AMP hydrolysis was estimated in blood taken before and after administration of glucagon. Glucagon (2 nmole/kg.) increased cyclic AMP hydrolysis slightly, but this was explained by the raised cyclic AMP levels. By contrast, cyclic AMP hydrolysis increased two-to-threefold in blood taken 20 and 40 minutes after glucagon (20 nmole/kg.). The higher dose of glucagon also stimulated cyclic AMP hydrolysis in crude liver homogenate, which could not be explained by increases in cyclic AMP concentration. The increase in cyclic AMP hydrolysis observed in blood and liver may partly explain the failure to show additional stimulation of hepatic and plasma cyclic AMP levels with the higher dose of glucagon. Despite the changes in cyclic AMP hydrolysis, a highly significant correlation was observed in individual rabbits between the hepatic and plasma cyclic AMP responses to glucagon (2 and 20 nmole/kg.), when these were calculated as incremental areas above mean basal levels. It is suggested that measurement of plasma cyclic AMP levels after stimulation by glucagon may be an accurate index of the hepatic cyclic AMP response to glucagon in vivo.

Animals↗

PubMed1978

Induction of cyclic AMP-binding proteins by dibutyryl cyclic AMP in mouse neuroblastoma cells.

Mouse neuroblastoma cells grown in the presence of 1 mM N6,O2'-dibutyryl-cyclic AMP showed a 3-fold increase in cyclic AMP-binding proteins. The role of dibutyryl cyclic AMP in the introduction of cyclic AMP-binding proteins in these cells has been studied. Induced cyclic AMP-binding proteins were observed in the cytoplasm 15 h after dibutyryl cyclic AMP treatment. The increase in cyclic AMP-binding proteins required RNA and protein synthesis. It is suggested that the 15-h lag occurs at the post-transcriptional and/or translational level. Cyclic AMP-binding proteins are found in both soluble and particulate cell fractions. Dibutyryl cyclic AMP increased binding proteins in both fractions. The control and dibutyryl cyclic AMP-induced binding proteins showed similar affinity for cyclic AMP. The data indicate that dibutyryl cyclic AMP caused the following sequential events: a 12-fold increase in cyclic AMP levels; a 40% increase in phosphodiesterase activity; and a 300% (3-fold) increase in cyclic AMP-binding proteins. It is suggested that the differentiation of mouse neuroblastoma cells involves increased levels of cyclic AMP and cyclic AMP-binding proteins.

3',5'-Cyclic-AMP Phosphodiesterases↗

PubMed1975

The role of cyclic AMP in the chemotactic responsiveness and spontaneous motility of rabbit peritoneal neutrophils. The inhibition of neutrophil movement and the elevation of cyclic AMP levels by catecholamines, prostaglandins, theophylline and cholera toxin.

Agents known to affect intracellular levels of cyclic AMP in many diverse systems have been tested for their effect on the chemotaxis induced by Escherichia coli culture filtrates, spontaneous motility and cyclic AMP levels of rabbit peritoneal neutrophils. Prostaglandin E1 and A1 but not prostaglandin F2alpha increased neutrophil cyclic AMP levels and, correspondingly, only the former two prostaglandins inhibited chemotaxis. Nevertheless, a quantitative relationship between prostaglandin stimulation of cyclic AMP and inhibition of chemotaxis could not be found. Epinephrine, isoproterenol, and, to a much lesser extent, norepinephrine increased neutrophil cyclic AMP through beta adrenergic stimulation. Only epinephrine and isoproterenol inhibited chemotaxis, but the inhibition was variable and not related to the ability of these catecholamines to increase intracellular cyclic AMP. Cholera toxin increased neutrophil cyclic AMP after a 30-min lag period which paralled its inhibitory effect on chemotaxis and spontaneous motility. However, the effect on chemotaxis require 50 ng/ml of toxin whereas the effect on cyclic AMP was manifested at 2 ng/ml of toxin. Prior to 30-min preincubation there was no effect of even 1250 ng/ml of toxin on either cyclic AMP or chemotaxis. Choleragenoid prevented the effects of toxin on both cyclic AMP and chemotaxis. The bacterial chemotactic factor obtained from E. coli culture filtrates did not effect a measurable change in levels of neutrophil cyclic AMP. The data indicate that even though cyclic AMP is not, in the main sequence of events, triggering the chemotactic response, increases in neutrophil cyclic AMP may modulate the movement and thus the chemotactic responsiveness of the neutrophil.

Animals↗

PubMed1991

Evidence that AMP triggers phosphorylation as well as direct allosteric activation of rat liver AMP-activated protein kinase. A sensitive mechanism to protect the cell against ATP depletion.

1. In freshly isolated rat hepatocytes, the activity of the AMP-activated protein kinase is high, but decreases by 5-10-fold during incubation of the cells for 60 min. The expressed activity of acetyl-CoA carboxylase is initially very low, then rises in a reciprocal manner to the AMP-activated protein kinase activity. For both enzymes, treatment of partially purified preparations under dephosphorylating conditions abolishes the difference in activity between freshly isolated and preincubated cells. Thus, both the high activity of the AMP-activated protein kinase and the low activity of acetyl-CoA carboxylase in freshly isolated cells can be explained by phosphorylation. 2. Immediately after isolation, the hepatocytes have AMP/ATP ratios that are unphysiologically high (approximately 1:1.5). During incubation of the cells for 60 min, AMP levels fall and ATP levels rise so that the ratio becomes about 1:15, close to previous estimates of the ratio in freeze-clamped liver. The fall in AMP/ATP ratio precedes the decrease in AMP-activated protein kinase activity. 3. In cells which have been incubated for 60 min, treatment with 20 mM fructose, which causes a large but transient increase in the AMP/ATP ratio, also causes concomitant activation of the AMP-activated protein kinase and inactivation of acetyl-CoA carboxylase. 4. In all cases described above, the increases in activity of acetyl-CoA carboxylase were blocked by treatment with the cell-permeable protein phosphatase inhibitor, okadaic acid. However, the decreases in activity of the AMP-activated protein kinase were not blocked by this inhibitor. This is consistent with the finding that okadaic-acid-insensitive protein phosphatase 2C is the most effective at dephosphorylating the kinase in cell-free assays. 5. The results above suggested that AMP either promotes phosphorylation, or inhibits dephosphorylation, of the kinase. Studies in a partially purified cell-free system suggested that the former hypothesis was correct; reactivation of dephosphorylated AMP-activated protein kinase by kinase kinase was completely dependent on the presence of AMP. 6. Our results, obtained in both intact cells and a cell-free system, suggest that rises in the AMP/ATP ratio promote phosphorylation of the AMP-activated protein kinase by the kinase kinase, as well as causing direct allosteric activation. This represents a very sensitive system for switching off lipid biosynthetic pathways when ATP levels are limiting. The results with okadaic acid also suggest that protein phosphatase 2C is mainly responsible for dephosphorylation of the AMP-activated protein kinase in intact hepatocytes.

AMP-Activated Protein Kinase Kinases↗

PubMed1976

Possible role of cyclic AMP in the relaxation process of mammalian heart: effects of dibutyryl cyclic AMP and theophylline on potassium contractures in cat papillary muscles.

The effect of dibutyryl cyclic AMP (DB-c-AMP; 3 X 10(-4)-3 X 10(-3) M) on electrically induced twitch and high potassium (142.4 mM KCl)-induced contracture tension was studied in papillary muscles from normal and reserpinized cats ([Ca]0 1.8 mM; 25 degrees C; pH 7.4). In both groups of preparations, the increase in twitch tension evoked by DB-c-AMP was accompanied by an abbreviation of the time to peak force and of relaxation time. In the same preparations, the high potassium contracture was markedly depressed by DB-c-AMP in a concentration-dependent manner. Similar results were obtained with the N6-monobutyryl derivative of cyclic AMP. The relaxing effects of the cyclic nucleotides on KCl contractures did not appear to be due to possible non-cyclic breakdown products: adenosine, 5'-AMP and sodium butyrate did not attenuate contracture tension at concentrations up to 3 X 10(-3) M. The same applies to ATP and non-cyclic N6-2'-0-3'-0-tributyryl-adenosine-monophosphate. Theophylline (10(-2) M) was found to prolong the relaxation time of the twitch and to enhance the high KCl contracture. It is concluded that cyclic AMP may be capable of modulating the relaxation process of mammalian heart and that not only the positive inotropic but also the relaxant effects of catecholamines on myocardium described before may be mediated by the cyclic AMP system. The relaxant effects of cyclic AMP derivatives on intact myocardial preparations are attributed to a stimulation by cyclic AMP of the calcium transport of the sarcoplasmic reticulum (SR) and are interpreted to be a corollary to the effects of cyclic AMP previously obtained on isolated SR preparations.

Animals↗

PubMed1979

Photoaffinity labeling of cyclic-AMP- and AMP-binding proteins differentiating Dictyostelium discoideum cells.

Cyclic-AMP-binding proteins play important roles during the differentiation of the cellular slime mold Dictyostelium discoideum. The photoaffinity reagent 8-N3-cyclic [32P]AMP has been used to label developmentally regulated cyclic-AMP-binding proteins of intact cells, membranes, and cytoplasm. 8-N3-Cyclic AMP is a chemoattractant for differentiated D. discoideum cells and is a substrate for the membrane phosphodiesterase (mPDE). When mPDE is inhibited, the only specifically labeled protein on intact cells has a molecular weight of 40,000 on sodium dodecyl sulfate gels. The developmental time course of appearance of this protein and its high specificity for cyclic AMP identify it as the cell surface chemotactic receptor for cyclic AMP. The concentration dependence of labeling of this protein is consistent with the measured chemotactic potency of 8-N3-cyclic AMP, which is about 1/100th that of cyclic AMP. Three developmentally regulated proteins (Mr 26,000, 33,000, and 36,000) of the soluble fraction (cytoplasm) are labeled by the photoaffinity reagent and are specific for cyclic AMP. By analogy with other systems, these may be regulatory subunits of protein kinases. The mPDE of ghosts or plasma membrane fractions converts the reagent to 8-N3-[32P]AMP, which specifically photoaffinity labels a protein of Mr 42,000 associated with the cytoplasmic face of the plasma membrane.

Affinity Labels↗

PubMed1978

Cyclic AMP levels and types I and II cyclic AMP-dependent protein kinase activity in synchronized cells and in quiescent cultures stimulated to proliferate.

Cyclic AMP as well as the specific activity of cyclic AMP-dependent protein kinase decreased from the first two hours after Chinese hamster ovary cells in plateau phase were stimulated to proliferate by tripsinization of confluent cultures and dilution in fresh media. From two to five hours after this stimulation, the cyclic AMP level and the specific activity of cyclic AMP-dependent protein kinase increased two-fold. There was a 40--50% increase in the degree of activation of cyclic AMP-dependent protein kinase during this same time interval. In plateau cultures prior to being stimulated to proliferate, type I cyclic AMP-dependent protein kinase was the predominant soluble form of these enzymes. At five hours after release from plateau, the predominant type of cyclic AMP-dependent protein kinase was type II. However, there was also a significant amount of type I present at this time. Types I and II cyclic AMP-dependent protein kinases were differentially detectable during the cell cycle of Chinese hamster ovary cells synchronized by mechanical selection of metaphase cells following colcemid treatment. During mitosis, type I kinase was predominant with only a small amount of type II activity detectable. The amount of activity of type I then progressively decreased as cells entered G1. During early G1, there was no detectable activity of type II kinase, but its activity increased from mid to late G1 and then decreased during the S phase. These data show a tight temporal relationship between the levels of cyclic AMP, the total cellular pool of type I and II cyclic AMP-dependent protein kinases, and the degree of activation of these kinases as cells traversed G1 toward S phase. These data suggest that the expression of each type of kinase may be important for the regulation of substrate phosphorylation during the cell cycle.

Animals↗

PubMed1990

Roles of the AMP-activated and cyclic-AMP-dependent protein kinases in the adrenaline-induced inactivation of acetyl-CoA carboxylase in rat adipocytes.

1. In isolated rat adipocytes, acetyl-CoA carboxylase is inactivated by treatment of the cells with adrenaline or the beta-agonist isoproterenol, but not by the alpha-agonist phenylephrine. The inactivation is stable during purification in the presence of protein phosphatase inhibitors, and is associated with a 30-40% increase in the labelling of enzyme isolated from 32P-labelled cells. 2. Increased phosphorylation occurs within peptide T1, which was identified by sequencing to be the peptide Ser-Ser77-Met-Ser79-Gly-Leu-His-Leu-Val-Lys, containing Ser-77 (phosphorylated by cyclic-AMP-dependent protein kinase) and Ser-79 (phosphorylated by the AMP-activated protein kinase). Analysis of the release of radioactivity as free phosphate during Edman degradation of peptide T1 revealed that all of the phosphate was in Ser-79 in both basal and hormone- or agonist-stimulated cells. Treatment of adipocytes with various agents which activate cyclic-AMP-dependent protein kinase by receptor-independent mechanisms (forskolin, cyclic AMP analogues, isobutylmethylxanthine) also produced inactivation of acetyl-CoA carboxylase and increased phosphorylation at Ser-79. 3. The (Rp)-[thio]phosphate analogue of cyclic AMP, which is an antagonist of binding of cyclic AMP to the regulatory subunit of cyclic-AMP-dependent protein kinase, opposes the effect of adrenaline on phosphorylation and inactivation of acetyl-CoA carboxylase. Together with the effects of isobutylmethylxanthine and the stimulatory cyclic AMP analogues, this strongly indicates that cyclic-AMP-dependent protein kinase is an essential component of the signal transduction pathway, although clearly it does not directly phosphorylate acetyl-CoA carboxylase. 4. As shown by okadaic acid inhibition, greater than 95% of the acetyl-CoA carboxylase phosphatase activity in extracts of rat adipocytes or liver is accounted for by protein phosphatase-2A, with less than 5% attributable to protein phosphatase-1. Inhibition of protein phosphatase-1 via phosphorylation of inhibitor-1 is therefore unlikely to be the mechanism by which cyclic-AMP-dependent protein kinase indirectly increases phosphorylation of acetyl-CoA carboxylase. Various other potential mechanisms are discussed.

1-Methyl-3-isobutylxanthine↗

PubMed1978

Role of cyclic AMP and protein kinase on the steroidogenic action of ACTH, prostaglandin E1 and dibutyryl cyclic AMP in normal adrenal cells and adrenal tumor cells from humans.

The role of the cyclic AMP-protein kinase system in mediating the steroidogenic effect of ACTH, prostaglandin E1 and dibutyryl cyclic AMP, induced similar stimulations of protein kinase activity, cyclic AMP was studied using human adrenal cells isolated from normal and adrenocortical secreting tumors. At high concentrations of ACTH, complete activation of protein kinase of normal adrenal cells was observed within 3 min, at the time when cyclic AMP production was slightly increased and there was still no stimulation of steroidogenesis. At supramaximal concentrations, ACTH, PGE1 and dibutyryl cyclic AMP and cortisol productions in adrenal cells isolated from normal and from one adrenocortical tumor. In one tumor in which the adenylate cyclase activity was insensitive to ACTH, the hormone was unable to stimulate protein kinase or steroidogenesis, but the cells responded to both PGE1 and dibutyryl cyclic AMP. In another tumor in which the adenylate cyclase was insensitive to PGE1, this compound also did not increase protein kinase activity or steroidogenesis, but both parameters were stimulated by ACTH and dibutyryl cyclic AMP. After incubation of normal adrenal cells with increasing concentrations of ACTH (0.01-100 nM) marked differences were found between cyclic AMP formation and cortisol production. However at the lowest concentrations of ACTH exerting an effect on steroid production a close linked correlation was found between protein kinase activation and cortisol production, but half-maximal and maximal cortisol production occurs at lower concentration of ACTH than was necessary to induce the same stimulation of protein kinase. Similar findings were found after incubating the adrenal cells with dibutyryl cyclic AMP (0.01-10 mM). The results implicate an important role of the cyclic AMP-protein kinase system during activation of adrenal cell steroidogenesis by low concentrations of steroidogenic compounds.

Adenylyl Cyclases↗

PubMed1978

The role of cyclic 3',5'-AMP in the regulation of aminoacyl-tRNA synthetase activities in mouse uterus and liver following 17beta-oestradiol treatment. Activation of a phosphoaminoacyl-tRNA synthetase phosphatase by phosphorylation with cyclic 3',5'-AMP dependent protein kinase.

The changes in the activities of 17 aminoacyl-tRNA synthetases induced by phosphorylation [1] were reversed by the action of cyclic AMP in preparations from both uterus and liver. Cyclic AMP also inhibited the phosphorylation of aminoacyl-tRNA synthetase protein by endogenous non-cyclic AMP-dependent protein kinase and [gamma-32P]ATP. The effect was not due to a stimulation of phosphoaminoacyl-tRNA synthetase phosphatase or to an influence of cyclic AMP on aminoacyl-tRNA synthetases. The activity of phosphoaminoacyl-tRNA synthetase phosphatase was increased by treatment with endogenous cyclic AMP-dependent protein kinase, ATP and cyclic AMP. Affinity chromatography of the 32P-labeled phosphorylated phosphosynthetase phosphatase protein followed by gel electrophoresis showed that the activated phosphatase was phosphorylated. In the uterus, the changes in 17 aminoacyl-tRNA synthetase activities observed 5 min after dibutyryl cyclic AMP administration to ovariectomized mice were similar to those observed after 17beta-oestradiol treatment, whereas in the liver the changes in these activities were the opposite to those found after treatment with 17beta-oestradiol. A mechanism for the regulation of the 17 aminoacyl-tRNA synthetase activities is proposed, which suggests that the synthetase activities inhibited (group I) or stimulated (group II) by phosphorylation with a non-cyclic AMP-dependent aminoacyl-tRNA synthetase kinase are reactivated (group I) or inhibited (group II), respectively, by the action of a cyclic AMP-dependent phosphatase kinase through the increased activity of phosphorylated phosphoaminoacyl-tRNA synthetase phosphatase.

Amino Acyl-tRNA Synthetases↗

PubMed1977

Effects of isoproterenol on cyclic AMP and cyclic AMP-dependent protein kinase in developing chick myocardium.

Embryonic chick (7-9 day) and newborn chick myocardia contain one major peak of cyclic AMP-dependent protein kinase activity as assessed by DEAE-cellulose chromatography. Evidence is presented that the cyclic AMP-dependent protein kinase activity ratios (activity in absence of cyclic AMP/activity in presence of added cyclic AMP) of homogenates prepared with low ionic strength buffer reflect the endogenous activation state of the enzyme. The cyclic AMP content of newborn chick myocardium is lower than that of 7--9 day embryonic chick myocardium; the baseline cyclic AMP-dependent protein kinase activity is correspondingly reduced. Isoproterenol produces smaller elevations in cyclic AMP and in the cyclic AMP-dependent protein kinase activity ratio of newborn chick as compared to embryonic chick myocardium. Differences in the ability of isoproterenol to elevate cyclic AMP in the different preparations are not accompanied by appropriate changes in the adenylate cyclase or phosphodiesterase activities of the corresponding broken cell preparations. Studies with the phosphodiesterase inhibitor, Ro 20 1724 indicate that the changes in the ability of isoproterenol to elevate cyclic AMP in the developing chick myocardium are due to changes in the metabolism of the cyclic nucleotide by phosphodiesterase.

4-(3-Butoxy-4-methoxybenzyl)-2-imidazolidinone↗

PubMed1992

A separation method for the assay of adenylylcyclase, intracellular cyclic AMP, and cyclic-AMP phosphodiesterase using tritium-labeled substrates.

A method for the separation of cyclic AMP from adenosine and polyvalent adenine nucleotides is described. The method consists of the sequential elution of adenosine and cyclic AMP from a single column of acidic aluminum oxide (alumina) with dilute hydrochloric acid and ammonium acetate. Adenosine, adenine, xanthine, and hypoxanthine are rapidly eluted with the application of 0.005 N hydrochloric acid while cyclic AMP remains adsorbed to the alumina. A subsequent application of 0.1 M ammonium acetate elutes more than 90% of the cyclic AMP. Under these conditions, polyvalent nucleotides (AMP, ADP, and ATP) remain adsorbed to the alumina. The method permits the measurement of adenylylcyclase activity using [3H]ATP as the labeled substrate. The same technique can be used to measure the accumulation of cyclic AMP in intact cells after labeling the ATP pool with [3H]adenine. With slight modification, the technique can be used to measure the activity of cyclic-AMP phosphodiesterase using [3H]cyclic AMP as the substrate. The proposed technique provides rapid, highly reproducible assays using inexpensive, disposable columns.

3',5'-Cyclic-AMP Phosphodiesterases↗

PubMed1977

Activation of rat erythrocyte phosphofructokinase by AMP and by non-physiological concentrations of cyclic AMP.

Cyclic AMP (300 micron) activates phosphofructokinase from dialyzed haemolysates of mature rat erythrocytes. The main conclusions are: a) Cyclic AMP, at pH 7.1 and low concentrations of fructose-6-phosphate, is able to reverse the inhibition produced by different amounts of ATP (up to 1.5 mM). b) The cyclic nucleotide is a positive allosteric effector of the enzyme as shown by the displacement of sigmoidal fructose-6-phosphate saturation curve to hyperbolic kinetics in the presence of inhibitory concentrations (1.5 mM) of ATP.c) Cyclic AMP has no significant influence as deinhibitor of phosphofructokinase either at pH 7.1 and non-inhibitory levels (0.25 mM) of ATP or at pH 8.1 and inhibitory (1.5 mM) or non-inhibitory (0.25 mM) concentrations of ATP. Similar conclusions were obtained with 300 micron AMP but not at a lower concentration (3 micron) with both nucleotides. The comparison of cyclic AMP result with those obtained under similar concentrations of AMP suggest that cyclic AMP is really only an "in vitro" modulator of the enzyme from rat erythrocytes, presumably at an AMP regulatory stie, since non-physiological concentrations are required to act as deinhibitor.

Adenosine Monophosphate↗

PubMed1977

Effects of cyclic AMP and dibutyryl cyclic AMP on cerebral hemodynamics and metabolism in the baboon.

Adenosine 3',5'-cycle monophosphate (cyclic AMP) (0.5 mg/kg) was infused into the carotid artery of baboons anesthesized with sodium pentobarbital, causing a biphasic increase in cerebral blood flow (CBF) and reduction in cerebrovascular resistance (CVR) associated in each phase with stimulation of cerebral metabolism evidenced by increased cerebral oxygen consumption (COMRO2) and cerebral glucose consumption (CMRG1). Intracarotid dibutyryl cyclic AMP (0.5 mg/kg) caused a monophasic increase in CBF and reduction of CVR but failed to alter cerebral metabolism. This may be due to its rapid removal from the circulation with ineffective passage across the blood-brain barrier since intracisternal infusion of dibutyryl cyclic AMP caused sustained increase in CBF, CMRO2 and CMRG1 and reduction in CVR. Intracarotid AMP (0.4 mg/kg) and adenosine (0.3 mg/kg) caused an immediate and more marked increase in CBF and decrease in CVR unassociated with cerebral metabolic change making it unlikely that the observed effects of cyclic AMP can be attributed to its breakdown products. Cyclic AMP or its dibutyryl derivative may alter cerebral metabolism secondary to neuronal activation but increase in glucose/oxygen utilization ratio after intracarotid cyclic AMP and intracisternal dibutytyl cyclic AMP also suggests an influence on enzymatic regulation of glucose metabolism.

Adenosine↗

PubMed1976

1,N6-etheno-AMP and 1,N6-etheno-2'-deoxy-AMP as probes of the activator site of glycogen phosphorylase from rabbit skeletal muscle.

Both 1,N6-etheno-AMP and 1,N6-etheno-2'-deoxy-AMP bind at the AMP site of phosphorylase b (1,4-alpha-D-glucan:orthophosphate alpha-glucosyltransferase, EC 2.4.1.1). Etheno-AMP induces the same activation as AMP, about 30-fold higher than the activation induced by etheno-dAMP. The fluorescence of etheno-AMP and etheno-dAMP is associated with the base moiety; therefore, when free in solution, the two derivatives have identical fluorescence properties. However, when bound to phosphorylase, the fluorescence of etheno-AMP is quenched more efficiently than the fluorescence of etheno-dAMP. This difference between the fluorescence properties of the bound nucleotides suggests that a modification in the ribose ring affects the position of the adenine in the AMP site of phosphorylase b. The observed quenching may be due to a stacking interaction between an aromatic residue and the base moiety of the bound nucleotide.

Adenosine Monophosphate↗

PubMed1978

Cyclic AMP binding proteins and cyclic AMP-dependent protein kinase from Blastocladiella emersonii.

The stoichiometry of cyclic AMP binding protein to cyclic AMP in sporulating cells of Blastocladiella emersonii and the resistance of protein-bound cyclic AMP to enzyme-catalyzed hydrolysis suggest that the distribution of cyclic AMP between free and protein-bound pools is an important factor in cyclic AMP metabolism. Most but not all of the cyclic AMP binding protein in sporulating cells is associated with a cyclic AMP-dependent protein kinase.

3',5'-Cyclic-AMP Phosphodiesterases↗

PubMed1992

Positive and negative control of ompB transcription in Escherichia coli by cyclic AMP and the cyclic AMP receptor protein.

The ompB operon encodes OmpR and EnvZ, two proteins that are necessary for the expression and osmoregulation of the OmpF and OmpC porins in Escherichia coli. We have used in vitro and in vivo experiments to show that cyclic AMP and the cyclic AMP receptor protein (CRP) directly regulate ompB. ompB expression in an ompB-lacZ chromosomal fusion strain was increased two- to fivefold when cells were grown in medium containing poor carbon sources or with added cyclic AMP. In vivo primer extension analysis indicated that this control is complex and involves both positive and negative effects by cyclic AMP-CRP on multiple ompB promoters. In vitro footprinting showed that cyclic AMP-CRP binds to a 34-bp site centered at -53 and at -75 in relation to the start sites of the major transcripts that are inhibited and activated, respectively, by this complex. Site-directed mutagenesis of the crp binding site provided evidence that this site is necessary for the in vivo regulation of ompB expression by cyclic AMP. Control of the ompB operon by cyclic AMP-CRP may account for the observed regulation of the formation of OmpF and OmpC by this complex (N. W. Scott and C. R. Harwood, FEMS Microbiol. Lett. 9:95-98, 1980).

Bacterial Outer Membrane Proteins↗