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)

Choleragen exerts its effect on cells through activation of adenylate cyclase. Choleragen initially interacts with cells through binding of the B subunit of the toxin to the ganglioside GM1 on the cell surface. Subsequent events are less clear. Patching or capping of toxin on the cell surface may be an obligatory step in choleragen action. Studies in cell-free systems have demonstrated that activation of adenylate cyclase by choleragen requires NAD. In addition to NAD, requirements have been observed for ATP, GTP, and calcium-dependent regulatory protein. GTP also is required for the expression of choleragen-activated adenylate cyclase. In preparations from turkey erythrocytes, choleragen appears to inhibit an isoproterenol-stimulated GTPase. It has been postulated that by decreasing the activity of a specific GTPase, choleragen would stabilize a GTP-adenylate cyclase complex and maintain the cyclase in an activated state. Although the holotoxin is most effective in intact cells, with the A subunit having 1/20th of its activity and the B subunit (choleragenoid) being inactive, in cell-free systems the A subunit, specifically the A1 fragment, is required for adenylate cyclase activation. The B protomer is inactive. Choleragen, the A subunit, or A1 fragment under suitable conditions hydrolyzes NAD to ADP-ribose and nicotinamide (NAD glycohydrolase activity) and catalyzes the transfer of the ADP-ribose moiety of NAD to the guandino group of arginine (ADP-ribosyltransferase activity). The NAD glycohydrolase activity is similar to that exhibited by other NAD-dependent bacterial toxins (diphtheria toxin, Pseudomonas exotoxin A), which act by catalyzing the ADP-ribosylation of a specific acceptor protein. If the ADP-ribosylation of arginine is a model for the reaction catalyzed by choleragen in vivo, then arginine is presumably an analog of the amino acid which is ADP-ribosylated in the acceptor protein. It is postulated that choleragen exerts its effects on cells through the NAD-dependent ADP-ribosylation of an arginine or similar amino acid in either the cyclase itself or a regulatory protein of the cyclase system.
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PMID:Mechanism of action of choleragen. 21 41

Escherichia coli heat-labile enterotoxin (labile toxin, LT) catalyzed the hydrolysis of NAD to ADP-ribose and nicotinamide and the ADP-ribosylation of arginine (Moss, J., and Richardson, S.H. (1978) J. Clin. Invest. 62, 281-285). Analysis of the product of the ADP-ribosylation of arginine by nuclear magnetic resonance spectroscopy indicated that the reaction was stereospecific and resulted in the formation of alpha-ADP-ribosyl-L-arginine. This reaction product rapidly anomerized to yield a mixture of the alpha and beta forms. In the presence of [adenine-U-14C]NAD, E. coli enterotoxin catalyzed the transfer of the radiolabel to proteins; the ADP-ribosylation of proteins was inhibited by arginine methyl ester, an alternative substrate. Digestion of the 14C-protein with snake venom phosphodiesterase released predominantly 5'-AMP. No product was obtained with a mobility similar to that of 2'-(5''-phosphoribosyl)-5'-AMP. This result is consistent with the covalent attachment by the enterotoxin of ADP-ribose rather than poly(ADP-ribose) to protein. Thus, LT is catalytically equivalent to choleragen, an enterotoxin of Vibrio cholerae, and activates adenylate cyclase through a similar stereospecific ADP-ribosylation reaction.
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PMID:NAD-dependent ADP-ribosylation of arginine and proteins by Escherichia coli heat-labile enterotoxin. 22 95

Upon incubation of lysed pigeon erythrocytes with NAD, adenosine diphosphate-ribose (ADP-ribose) is incorporated into nuclear poly ADP-ribose and into an unidentified acid-insoluble product of the cytosol. The properties of these incorporations have been examined and a method developed for reducing their amount whilst retaining the sensitivity of the lysate to cholera toxin. This method has allowed the detection and description of a set of cholera toxin-specific ADP-ribose transfers to membrane-bound and soluble proteins under conditions that lead to adenylate cyclase activation.
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PMID:Cholera toxin-catalysed ADP-ribosylation of erythrocyte proteins: general properties. 22 65

GTP evoked both an activatory and an inhibitory response from adipocyte adenylate cyclase. This paper describes the persistence of the bimodal response under a variety of assay conditions. Additionally, manipulations are described which eliminate one or other of these actions. Treatment of adipocyte plasma membranes with cholera toxin A1 peptide and NAD+ abolishes the inhibitory phase of GTP action while preserving the activating phase. Treatment of the membranes with p-hydroxymercuriphenylsulfonic acid eliminates the activatory phase while maintaining the inhibitory processes mediated by GTP in adipocytes normally coexist and operate through different pathways since either phase can be abolished leaving the other intact. Adenosine and its purine-modified analogs inhibit fat cell adenylate cyclase in the GTP inhibitory phase (Londos, C., Cooper, D. M. F., Schlegel, W., and Rodbell, M. (1978) Proc. Natl. Acad. Sci. U.S.A. 75, 5362-5366). When this effect of GTP is abolished by either cholera toxin or Gpp(NH)p pretreatment, the inhibitory action of adenosine analogs is also lost. These data suggest a central role for GTP in mediating both activation and inhibition of adenylate cyclase by agents which act through cell surface receptors.
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PMID:The fat cell adenylate cyclase system. Characterization and manipulation of its bimodal regulation by GTP. 22 17

There is a positive correlation between lactate output and insulin secretion but there is no correlation between total islet PEP content and insulin secretion and no correlation between cAMP production and insulin release. Neither PEP or cAMP seem to be primary triggers to insulin release but may rather act as positive modulators of insulin secretion. Potentially, PEP can maintain an elevated cytoplasmic Ca++ concentration by inhibiting Ca++ uptake in the mitochondria, increase the concentration of cAMP in the beta-cells by activating the adenylate cyclase (11) and change the phosphorylation state of the plasma membrane (12). The possible trigger effect of an increased glycolytic flux on insulin secretion may be mediated perhaps via changes in the NADH/NAD+ ratio (13). As regards the mechanism of potentiation of insulin release: in the fed state potentiation may be related to an increased glycolytic flux whereas this is not the case during starvation. Here enhancement of cAMP may play a role.
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PMID:The role of phosphoenolpyruvate and lactate production in insulin secretion. 22 40

Treatment of cultured normal rat kidney cells with the nitrosourea-containing compounds streptozotocin, chlorozotocin, or 1-(2-chloroethyl)-3-(4-methylcyclohexyl)-1-nitrosourea resulted in a time-dependent potentiation in the ability of prostaglandin E1 and (-)-isoproterenol to elevate intracellular cAMP levels. This hormone response increased at 4 hours and reached a maximum at 15--25 hours after addition of the nitrosoureas. Basal cAMP levels were not affected. The greater response was apparently due to an increase in the GTP-dependent step in hormonal activation of adenylate cyclase, inasmuch as GTP- and GTP plus hormone-stimulated adenylate cyclase activities were enhanced twofold to threefold in crude membranes prepared from nitrosourea-treated cells. Fluoride-stimulated adenylate cyclase activity was increased only 10--25%. Nicotinamide did not prevent the elevated response, and NAD+ plus NADH levels were not appreciably altered after 42 hours; treatment with streptozotocin. The results suggest a possible involvement of cAMP in the biologic actions of nitrosoureas.
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PMID:Increase in hormonal activation of adenylate cyclase by treatment of cultured cells with N-alkyl,N-nitrosourea. 22 93

A method is described for the isolation of secondary lysosomes from homogenates of rabbit liver; The uptake of Triton WR-1339 by rabbit-liver lysosomes when administered by intraperitoneal injection was used to decrease the density of secondary lysosomes. Lysosomal fractions prepared by this method contain an NAD nucleosidase (NAD glycohydrolase, EC 3;2.25), an enzyme which has previously been considered to be associated with other subcellular fractions. The enzyme has maximum activity at pH 6 and cleaves both NAD and NADP. It is inhibited by nicotinamide (Ki equals 4.5 mM) and by HgCl2. Both nucleosidase and 2'-nucleotidase show in-vitro latency typical of lysosomal acid hydrolases. Rabbit-liver plasma-membrane fractions were isolated which contained most 5'-nucleotidase but relatively little nucleosidase, whereas rabbit liver lysosomes contain both 5'-nucleotidase and nucleosidase enzymes but little adenyl cyclase.
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PMID:Evidence for NAD nucleosidase in rabbit-liver lysosomes. 23 77

Various serine proteases (e.g., trypsin, alpha-chymotrypsin, Pronase, and subtilisin) stimulate adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] activity in a membrane-enriched fraction of the rat ovary. Maximum stimulation is observed at protease concentrations ranging from 3 to 10 mug/ml. Higher protease concentrations inhibit ovarian adenylate cyclase in a dose-dependent manner. Protease stimulation causes a 6- to 8-fold increase in adenylate cyclase activity, which is comparable to the stimulation observed with human chorionic gonadotropin. Combinations of trypsin plus hormone or trypsin plus NaF stimulate ovarian adenylate cyclase activity to a greater extent than does any one of these alone. The mechanism of protease stimulation of adenylate cyclase involves limited proteolysis because zymogen precursors fail to activate the cyclase as does trypsin pretreated with trypsin inhibitors. Unlike cholera toxin, the serine protease stimulation is immediate (within the first 5 min) and requires no additional factors (e.g., NAD(+)). It is unlikely that protease stimulation of adenylate cyclase results from a proteolytic modification of the hormone receptor on the cell surface, because of the additive effects noted above and because protease stimulation is also observed in ovaries desensitized to hormone that lack this hormone receptor. Results with Lubrol-treated membranes also suggest that proteolytic enzymes do not directly activate the catalytic subunit of the cyclase or unmask new catalytic sites because the protease effect (like hormonal stimulation) is abolished by the detergent, whereas fluoride stimulation is enhanced. Other data suggest that serine protease and chorionic gonadotropin stimulation of adenylate cyclase result from activation of a membrane protease that then regulates adenylate cyclase in the ovary.
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PMID:Proteolytic enzyme activation of rat ovarian adenylate cyclase. 27 Jul 17

Incubation of fat cell ghosts with activated cholera toxin, nucleoside triphosphate, cytosol, and NAD results in increased adenylate cyclase activity and the transfer of ADP-ribose to membrane proteins. The major ADP-ribose protein comigrates on sodium dodecyl sulfate-polyacrylamide gels with the putative GTP-binding protein of pigeon erythrocyte membranes (Mr 42 000), which is also ADP-ribosylated by cholera toxin. The treatment with cholera toxin enhances the stimulation of the fat cell membrane adenylate cyclase by GTP, but the stimulation by guanyl-5'-yl imidodiphosphate is unaltered. Subsequent stimulation of fat cell adenylate cyclase by 10 micrometers epinephrine is not particularly affected. These changes were qualititatively the same for membranes isolated from fat cells of hypothyroid rats. Although the cyclase of these membranes has a reduced response to epinephrine, guanyl-5'-yl imidodiphosphate or GTP, as compared to euthyroid rat fat cell membranes, the defect is not rectified by toxin treatment and cannot be explained by a deficiency in the cholera toxin target.
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PMID:ADP-ribosylation of membrane proteins and activation of adenylate cyclase by cholera toxin in fat cell ghosts from euthyroid and hypothyroid rats. 47 51

The role of cytosol components in the loss of rat liver adenylate cyclase activity which occurs during the preparation of particulate fractions from crude homogenates was studied. Epinephrine (5 micron)-, glucagon (10 micron)-, and fluoride (5 mM)- stimulated activities of twice-washed particulates were 31%, 58% and 67% of the homogenate activities, respectively. Addition of cytosol (100,000 X g supernatant devoid of adenylate cyclase activity) restored these activities to 82%, 88% and 80%. Cytosol also increased particulate basal activity from 60% of homogenate activity to 98%. The cytosol components capable of increasing adenylate cyclase activity were heat labile, nondialyzable, stable to freezing at -20 degrees, resistant to change of pH between 2 and 12, and unaffected by EGTA and NAD. Pretreatment with pepsin destroyed the effects of cytosol on both epinephrine- and glucagon-sensitive activities, whereas trypsin destroyed the effect of cytosol only on epinephrine-sensitive activity. The cytosol effect on adenylate cyclase was specific, since several purified proteins and ubiquitin, did not stimulate enzyme activity. Only part of the cytosol effect could be attributed to its GTP content. GTP at the concentration present in cytosol stimulated epinephrine-sensitive activity but significantly less than did cytosol, while GTP had no effect on glucagon-sensitive activity. Dialyzed cytosol retained its effectiveness even after removal of most (97%) of its GTP to a concentration where GTP had only a minimal effect on epinephrine-sensitive activity. Cytosol, unlike GTP, stimulated rather than inhibited activation by fluoride. Cytosol thus appears to contain at least two different protein components, which increase the activity of the two hormone-sensitive adenylate cyclases and presumably account in part for losses of adenylate cyclase activities seen during the preparation of particulates from homogenates.
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PMID:Activation of epinephrine and glucagon-sensitive adenylate cyclases of rat liver by cytosol protein factors. Role in loss of enzyme activities during preparation of particulate fractions, quantitation and partial characterization. 72 79


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