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 activities of adenylate and guanylate cyclase and cyclic nucleotide 3':5'-phosphodiesterase were determined during the aggregation of human blood platelets with thrombin, ADP, arachidonic acid and epinephrine. The activity of guanylate cyclase is altered to a much larger degree than adenylate cyclase, while cyclic nucleotide phosphodiesterease activity remains unchanged. During the early phases of thrombin-and ADP-induced platelet aggregation a marked activation of the guanylate cyclase occurs whereas aggregation induced by arachidonic acid or epinephrine results in a rapid diminution of this activity. In all four cases, the adenylate cyclase activity is only slightly decreased when examined under identical conditions. Platelet aggregation induced by a wide variety of aggregating agents including collagen and platelet isoantibodies results in the "release" of only small amounts (1-3%) of guanylate cyclase and cyclic nucleotide phosphodiesterase and no adenylate cyclase. The guanylate cyclase and cyclic nucleotide phosphodiesterase activities are associated almost entirely with the soluble cytoplasmic fraction of the platelet, while the adenylate cyclase if found exclusively in a membrane bound form. ADP and epinephrine moderately inhibit guanylate and adenylate cyclase in subcellular preparations, while arachidonic and other unsaturated fatty acids moderately stimulate (2-4-fold) the former. It is concluded that (1) the activity of platelet guanylate cyclase during aggregation depends on the nature and mode of action of the inducing agent, (2) the activity of the membrnae adenylate cyclase during aggregation is independent of the aggregating agent and is associated with a reduction of activity and (3) cyclic nucleotide phosphodiesterase remains unchanged during the process of platelet aggregation and release. Furthermore, these observations suggest a role for unsaturated fatty acids in the control of intracellular cyclic GMP levels.
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PMID:Cyclic nucleotides and platelet aggregation. Effect of aggregating agents on the activity of cyclic nucleotide-metabolizing enzymes. 0 49

ADP-induced platelet aggregation and shape change were monitored optically in citrated rabbit platelet-rich plasma (PRP) diluted with isotonic salt solutions. Lithium (Li) produced a concentration-dependent reduction in the rate of platelet aggregation but had no discernible effect on the shape change which precedes aggregation. When PRP was pre-incubated with Li, the inhibitory effect of the ion was independent of the duration and temperature of the treatment. The inhibitory effect of Li also was observed in heparinized PRP or when 5-HT was used as the aggregation-inducing agent. When Li was combined with aggregation inhibitors which enhance platelet cyclic AMP content either by activating adenylate cyclase or by inhibiting phosphodiesterase, only additive effects were observed. The inhibitory effect of Li was opposed by added calcium. Kinetic evaluation of the interaction between Li and Ca indicated that their antagonism was competitive. Added calcium also displayed competitive antagonism toward the aggregation inhibiting effect of increased hydrogen ion concentration in the pH range between 6 and 8.
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PMID:Competitive inhibition by lithium and hydrogen ions of the effect of calcium on the aggregation of rabbit platelets. 1 92

1. The prior addition of non-aggregating concentrations of the divalent cation ionophore, A-23187, causes human platelets to aggregate in response to a subsequent addition of the 2',3'-dialdehyde and 2',3'-dialcohol derivatives of ADP (oADP and or ADP). Previous studies [Pearce et al. (1978) Eur. J. Biochem. 88, 543--555] have shown that these derivatives act as partial agonists at the platelet ADP receptor inducing only the transition from discoid to globular morphology ('shape change'). A secretion response is also observed on addition of a low concentration of ionophore A-23187 prior to orADP. These responses are not observed if ionophore A-23187 is added prior to the 2',3'-dialdehyde and 2',3'-dialcohol derivatives of ATP (oATP and or ATP) and are markedly inhibited by prior addition of the ADP antagonist, adenosine 5'-[beta, gamma-methylene]triphosphate. 2. The aggregation response to oADP in the presence of ionophore A-23187 is reduced but not eliminated by addition of 3 mM EGTA when studies are performed in heparinised platelet-rich plasma. Additions of 3 mM EGTA in citrated platelet-rich plasma, or of 4 mM EDTA in either system completely inhibits this response. Inhibitors which are reported to elevate the intracellular concentration of adenosine 3':5'-monophosphate (cyclic AMP) or to prevent Ca2+ movement also inhibit the aggregation response to oADP which is observed in the presence of ionophore A-23187. 3. Prior addition of inhibitors of adenylate cyclase fails to cause an aggregation response to subsequent addition of oADP or orADP. Certain of these inhibitors enhance and prolong the shape change response to oADP or orADP but only at concentrations an order of magnitude in excess of those required to antagonise inhibition by agents such as prostaglandin E1, which act by increasing the concentration of cyclic AMP. 4. The concentration of prostaglandin E1, adenosine or papaverine required to inhibit shape change induced by oADP is one to two orders of magnitude lower than that required to inhibit shape change induced by ADP. 5. Prior addition of oADP decreases the lag phase in the response of human platelets to arachidonate while also increasing the concentration required to observe half-maximal response, and causing a decrease in the extent of the response. Prior addition of oATP also diminishes the extent of this response and increases the concentration of arachidonate required but has no effect on the lag phase. 6. The data suggest that oADP and orADP are capable only of acting as partial agonists at the ADP receptor because of a defective ability to increase cytosolic Ca2+ concentration. The defect is rectified by the presence of low concentrations of ionophore A-23187, which promotes mobilisation of Ca2+ from an intracellular store. The results do not appear consistent with the thesis that a decrease in platelet cyclic AMP is an initiating event in aggregation induced by ADP, but do support a model which implicates cyclic AMP in depletion of cytosolic Ca2+.
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PMID:Factors influencing the response of human blood platelets to analogues of ADP which may act as partial agonists at the ADP receptor. 11 May 86

Different antiarrhythmic agents such as quinidine, procaine amide, and lodocaine at 1 mM concentrations were found to depress the ability of an isolated perfused rat heart to generate contractile force. Quinidine, but not procaine amide or lidocaine, decreased calcium uptake by both mitochondrial and microsomal fractions at different concentrations of calcium. The mitochondrial phosphorylation rate, respiratory control index, and state 3 oxygen consumption, but not ADP:O ratio and state 4 oxygen consumption, were depressed by only quinidine. None of these agents had any effect on myofibrillar Mg2+-ATPase or Ca2+-stimulated ATPase activities. On the other hand, sarcolemmal Mg2+-ATPase and Ca2+-ATPase activities, but not Na+-K+-ATPase activity, were increased by all these drugs. The sarcolemmal adenylate cyclase (EC 4.6.1.1) activity was decreased by quinidine only. These results suggest some similarities and differences in the sites of action of quinidine, procaine amide, and lidocaine within the myocardium.
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PMID:Subcellular and functional effects of quinidine, procaine amide, and lidocaine on rat myocardium. 13 Sep 65

Choleragen catalyzed the hydrolysis of NAD to ADP-ribose and nicotinamide; nicotinamide production was dramatically increased by L-arginine methyl ester and to a lesser extent by D- or L-arginine, but not by other basic amino acids. Guanidine was also effective. Nicotinamide formation in the presence of L-arginine methyl ester was greatest under conditions previously shown to accelerate the hydrolysis of NAD by choleragen (Moss, J., Manganiello, V. C., and Vaughan, M. (1976) Proc. Natl. Acad. Sci. U.S.A. 73, 4424-4427). After incubation of [adenine-U14C]NAD and L[3H]arginine with coleragen, a product was isolated by thin layer chromatography that contained adenine and arginine in a 1:1 ratio and has been tentatively identified as ADP-ribose-L-arginine. Parallel experiments with [carbonyl-14C]NAD have demonstrated that formation of the ADP-ribosyl-L-arginine derivative was associated with the production of [carbonyl-14C]nicotinamide. As guanidine itself was active and D- and L-arginine was equally effective in promoting nicotinamide production, whereas citrulline, which possesses a ureido rather than a guanidino function, was inactive, it seems probable that the guanidino group rather than the alpha-amino moiety participated in the linkage to ADP-ribose. Based on the assumption that the ADP-ribosylation of L-arginine by choleragen is a model for the NAD-dependent activation of adenylate cyclase by choleragen, it is proposed that the active A protomer of choleragen catalyzes the ADP-ribosylation of an arginine, or related amino acid residue in a protein, which is the cyclase itself or is critical to its activation by choleragen.
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PMID:Mechanism of action of choleragen. Evidence for ADP-ribosyltransferase activity with arginine as an acceptor. 13 9

6.1. It is known from the literature that in diabetes mellitus there is an increased tendency for the thrombocytes to aggregate. This fact represents a risk of thrombosis supplementary to the vascular wall lesions which develop in the course of this disease. An inhibition of platelet aggregation such as has recently been obse3rved in vitro under the influence of beta-cytotropic sulphonylureas (tolbutamide, glicalazide), must therefore be regarded as an additional, desired quality of action of these agents. 6.2. In an attempt to throw more light on this subject studies were conducted to discover whether an inhibition of platelet aggregation can be regarded as a basic property of all beta-cytotropic antidiabetic agents and whether dissociation exists between this property and the hypoglycemic effect. The possible existence of evidence for identical or similar sites of action of sulphonylureas on the control system of the thrombocytes, beta-cells and the liver was also investigated, the main point of interest being whether sulphonylurea derivatives exert their effects via the adenylate cyclase -cAMP-system. The thrombocytes were also used to discover whteher ss-cytotropic antidiabetic agents, such as non-steroidal antiphlogistic compounds, inhibit the synthesis of aggregation-promoting prostaglandins (PGE2). 6.3. The influence on adenosine diphosphate (ADP)-induced thrombocyte aggregation has been dtudied in vitro with platelet rich rat plasma (PRP) using a turbidimetric method. Preliminary studies have also been conducted with PRP obtained after previous treatment of the donor animals...
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PMID:[Mechanisms of platelet aggregation inhibition caused by sulfonylurea compounds. 4. Discussion, summary, and literature]. 16 7

Plasma membranes were isolated from bovine renal cortex. This particulate, adenylate cyclase-containing fraction was stimulated to produce cyclic AMP by parathyroid hormone and fluoride. When the time-course of adenylate cyclase activity was investigated, it was found that while PTH-stimulated cyclic AMP production comes to a halt in about 15 minutes after the initiation of the reaction, fluoride-stimulated activity continues unabated for at least an hour. Experiments to determine the cause of this showed that the cyclase enzyme is not degraded under our experimental conditions, but is inhibited by a soluble, unbound product of the reaction which requires ATP for its synthesis. In our experiments degradation of parathyroid hormone was relatively slow and could not account for the rapid inhibition of PTH-stimulated cyclase activity. Of the various agents tested, cyclic AMP was found capable of inhibiting PTH-stimulated cyclic AMP production by our purified membrane preparation. Half-maximal inhibition was observed at around 10(-6) M concentrations of the nucleotide. Pyrophosphate, adenosine, 5'-AMP and ADP had no effects. The significance of these results in relation to the regulation of adenylate cyclase activity is discussed.
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PMID:Inhibition of a parathyroid hormone-stimulated renal adenylate cyclase by cyclic AMP. 17 12

A method is developed for micro-scale separation of the products of enzymatic degradation of ATP (ADP, 5'-AMP, adenosine 3',5'-cytophosphate, adenosine and adenine) by one-dimentional thin-layer chromatography on Silufol UV-254 plates. The method is applicable for determination of activity of adenylate cyclase and of other enzymes involved in metabolism of adenylic derivatives, including the diesterase of 3',5'-cyclic AMP.
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PMID:[A micromethod for determination of the adenylate cyclase activity by chromatography on silufol UV-254 plates]. 17 4

Testicular and cauda epididymal sperm were obtained via catheters previously implanted in the rete testis and proximal vas deferens of bulls and were used to examine the relationships among sperm motility, cyclic adenosine 3':5'-monophosphate (cAMP) level, adenine nucleotide levels, and rates of glucose and oxygen consumption. Testicular, cauda epididymal, and ejaculated sperm contain cAMP-stimulated protein kinase, adenylate cyclase, and nucleotide phosphodiesterase. Treatment of the nonmotile testicular sperm with phosphodiesterase inhibitors resulted in a doubling of cellular cAMP concentration and a 25% increase in their glucose consumption. No change in motility, ATP level, or rate of oxygen consumption was observed. Sperm in neat cauda epididymal semen had flagellating tails but no progressive motility. Dilution of these sperm into glucose-containing buffer resulted in an increase in intracellular cAMP concentration and a decrease in ATP level with concomitant increases in ADP and AMP levels. These biochemical changes occurred within 30 s after dilution and apparently preceded the initiation of progressive motility by most cells. Since sperm in neat cauda epididymal semen became progressively motile when diluted with neat cauda epididymal plasma as well as accessory sex gland fluid or buffer, composition of the fluid surrounding the sperm is not responsible for the initiation of progressive motility upon dilution nor does cauda epididymal plasma contain an inhibitory factor. Perhaps release from contact immobilization provides the stimulation for the initial acquisition of progressive motility by cauda epididymal sperm. We conclude that during epididymal passage sperm develop from a cell physically unresponsive to changes in cAMP concentration to a form which initiates progressive motility upon changes in cAMP concentration.
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PMID:Adenine nucleotide changes at initiation of bull sperm motility. 17 61

Adenosine inhibits the aggregation of human but not of rat platelets whereas both are inhibited by prostaglandin E1 or by the pyrimido-pyrimidine compound RA233. In human platelets all three agents increase adenosine-3'-5'-cyclic monophosphate (cAMP). If the inhibition of aggregation depended on this increase, adenosine might be expected not to increase cAMP in rat platelets. Under conditions in which adenosine inhibited aggregation and increased cAMP in human platelets, adenosine caused a similar increase in cAMP in rat platelets without inhibiting their aggregation. The aggregation of rat platelets was inhibited as effectively as that of human platelets by PGE1 or RA233 at concentrations which caused greater increases in cAMP than did the highest concentrations (2.8 X 10(-4) M) of adenosine it was possible to use. When the increase of cAMP in rat platelets by PGE1 was limited to that produced by adenosine, PGE1 like adenosine failed to inhibit aggregation. Therefore, the difference in the inhibitory effectiveness of adenosine on rat and human platelets was quantitative rather than qualitative and apparently depended on the inability of adenosine to increase cAMP sufficiently in rat platelets. When cAMP had been increased by adenosine, PGE1 or RA233, the addition of ADP caused cAMP to decrease rapidly in both human and rat platelets to between +22 and -18% of control values, except that the decrease in rat platelets was to +40% after RA233 had been present for 0.5 min before ADP. The increase in cAMP produced in rat platelets by adenosine at 5 X 10(-6) to 2.8 X 10(-4) M for 3 min was associated with a small increase in aggregation velocity. It is suggested that the comparative ineffectiveness of adenosine as an inhibitor of platelet aggregation, particularly with rat but less so also with human platelets, is because, unlike PGE1 or RA233, adenosine has two opposing actions on aggregation; one being inhibition by activating adenylate cyclase and increasing cAMP, and the other being potentiation by uptake. This hypothesis accounts for the present results as well as for the earlier observation that dipyridamole which prevents the uptake of adenosine potentiates its inhibitory effect on the aggregation of human platelets.
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PMID:Relation between the inhibition of aggregation and the concentration of cAMP in human and rat platelets. 17 42


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