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Article: Evidence for interdependent action of glucagon and nucleotides on the hepatic adenylate cyclase system

TitleEvidence for interdependent action of glucagon and nucleotides on the hepatic adenylate cyclase system
Authors
Issue Date1974
PublisherAmerican Society for Biochemistry and Molecular Biology, Inc. The Journal's web site is located at http://www.jbc.org/
Citation
Journal Of Biological Chemistry, 1974, v. 249 n. 1, p. 59-65 How to Cite?
AbstractThe kinetic characteristics of glucagon action and binding as functions of hormone and nucleotide concentrations were investigated in the hepatic adenylate cyclase system. Either App(NH)p (5 adenylylimidodiphosphate), 0.1 mM, or adenosine triphosphate, 2 mM, was used as a substrate. The formation of adenosine 3':5' monophosphate (cyclic AMP) in response to glucagon exhibits lag times as long as 4 min in the presence of about 0.1 nM glucagon. The lag times diminish as the hormone or substrate concentrations increase. Addition of guanosine triphosphate (GTP) (0.1 mM) abolishes the lags at all concentrations of glucagon tested in the presence of 0.1 mM App(NH)p and causes a decrease in the concentration of glucagon required for half maximal activation of the enzyme. In the presence of GTP, the apparent K(m) for glucagon action ranges from 0.2 to 0.5 nM glucagon; in its absence, the K(m) ranges from 2 to 7 nM. Pretreatment of the enzyme system with glucagon for 15 min prior to addition of substrate also abolishes the lags seen at low concentrations of the hormone. When the pretreated enzyme system is incubated with limiting concentrations of substrate (0.1 mM App(NH)p) in the absence of free hormone, the velocity of enzyme activity is dependent upon GTP. Stimulatory effects are observed with 30 nM GTP; GTP exerts maximal effects at 1 μm. The lag times observed in onset of glucagon activation appear to reflect a change in state of the enzyme induced by glucagon binding to its receptor. The time dependency is changed simply by increasing the concentration of glucagon; GTP acts subsequent to or attendant upon this change in state induced by glucagon. Glucagon binding exhibits Hill coefficients of about 1.5, suggesting cooperative interactions between two or more subunits of the system. GTP, in addition to its effects on glucagon action, stimulates the rate of dissociation of glucagon from its receptor and, as a consequence, causes a decrease in the steady state levels of bound glucagon. The release of hormone seems not to be causally related to enzyme activation since the rates of dissociation are increased by addition of 0.1 mM GTP without concomitant increases in enzyme velocity. A hyperbolic relationship is observed between the levels of receptors occupied by glucagon and adenylate cyclase activity generated in the presence of GTP. Complete activation of the enzyme requires full occupation of the specific binding sites in hepatic plasma membranes (about 3 pmoles per mg of membrane protein). This finding shows that all of the specific binding sites for glucagon in these membranes represent receptors functionally and structurally linked to the adenylate cyclase system. The finding that glucagon and GTP activate adenylate cyclase by a concerted or interdependent mechanism is discussed in relation to the characteristics of the adenylate cyclase system as an allosteric regulatory enzyme system.
Persistent Identifierhttp://hdl.handle.net/10722/167426
ISSN
2015 Impact Factor: 4.258
2015 SCImago Journal Rankings: 3.151
ISI Accession Number ID

 

DC FieldValueLanguage
dc.contributor.authorRodbell, Men_US
dc.contributor.authorLin, MCen_US
dc.contributor.authorSalomon, Yen_US
dc.date.accessioned2012-10-08T03:06:50Z-
dc.date.available2012-10-08T03:06:50Z-
dc.date.issued1974en_US
dc.identifier.citationJournal Of Biological Chemistry, 1974, v. 249 n. 1, p. 59-65en_US
dc.identifier.issn0021-9258en_US
dc.identifier.urihttp://hdl.handle.net/10722/167426-
dc.description.abstractThe kinetic characteristics of glucagon action and binding as functions of hormone and nucleotide concentrations were investigated in the hepatic adenylate cyclase system. Either App(NH)p (5 adenylylimidodiphosphate), 0.1 mM, or adenosine triphosphate, 2 mM, was used as a substrate. The formation of adenosine 3':5' monophosphate (cyclic AMP) in response to glucagon exhibits lag times as long as 4 min in the presence of about 0.1 nM glucagon. The lag times diminish as the hormone or substrate concentrations increase. Addition of guanosine triphosphate (GTP) (0.1 mM) abolishes the lags at all concentrations of glucagon tested in the presence of 0.1 mM App(NH)p and causes a decrease in the concentration of glucagon required for half maximal activation of the enzyme. In the presence of GTP, the apparent K(m) for glucagon action ranges from 0.2 to 0.5 nM glucagon; in its absence, the K(m) ranges from 2 to 7 nM. Pretreatment of the enzyme system with glucagon for 15 min prior to addition of substrate also abolishes the lags seen at low concentrations of the hormone. When the pretreated enzyme system is incubated with limiting concentrations of substrate (0.1 mM App(NH)p) in the absence of free hormone, the velocity of enzyme activity is dependent upon GTP. Stimulatory effects are observed with 30 nM GTP; GTP exerts maximal effects at 1 μm. The lag times observed in onset of glucagon activation appear to reflect a change in state of the enzyme induced by glucagon binding to its receptor. The time dependency is changed simply by increasing the concentration of glucagon; GTP acts subsequent to or attendant upon this change in state induced by glucagon. Glucagon binding exhibits Hill coefficients of about 1.5, suggesting cooperative interactions between two or more subunits of the system. GTP, in addition to its effects on glucagon action, stimulates the rate of dissociation of glucagon from its receptor and, as a consequence, causes a decrease in the steady state levels of bound glucagon. The release of hormone seems not to be causally related to enzyme activation since the rates of dissociation are increased by addition of 0.1 mM GTP without concomitant increases in enzyme velocity. A hyperbolic relationship is observed between the levels of receptors occupied by glucagon and adenylate cyclase activity generated in the presence of GTP. Complete activation of the enzyme requires full occupation of the specific binding sites in hepatic plasma membranes (about 3 pmoles per mg of membrane protein). This finding shows that all of the specific binding sites for glucagon in these membranes represent receptors functionally and structurally linked to the adenylate cyclase system. The finding that glucagon and GTP activate adenylate cyclase by a concerted or interdependent mechanism is discussed in relation to the characteristics of the adenylate cyclase system as an allosteric regulatory enzyme system.en_US
dc.languageengen_US
dc.publisherAmerican Society for Biochemistry and Molecular Biology, Inc. The Journal's web site is located at http://www.jbc.org/en_US
dc.relation.ispartofJournal of Biological Chemistryen_US
dc.subject.meshAdenine Nucleotides - Pharmacologyen_US
dc.subject.meshAdenylate Cyclase - Metabolismen_US
dc.subject.meshAnimalsen_US
dc.subject.meshBinding Sitesen_US
dc.subject.meshCell Membrane - Drug Effects - Enzymologyen_US
dc.subject.meshChromatography, Ion Exchangeen_US
dc.subject.meshCyclic Amp - Biosynthesisen_US
dc.subject.meshGlucagon - Pharmacologyen_US
dc.subject.meshGuanosine Triphosphate - Pharmacologyen_US
dc.subject.meshIodine Radioisotopesen_US
dc.subject.meshKineticsen_US
dc.subject.meshLiver - Cytology - Drug Effects - Enzymologyen_US
dc.subject.meshPhosphorus Radioisotopesen_US
dc.subject.meshProtein Bindingen_US
dc.subject.meshRatsen_US
dc.subject.meshReceptors, Cell Surface - Drug Effectsen_US
dc.subject.meshTime Factorsen_US
dc.titleEvidence for interdependent action of glucagon and nucleotides on the hepatic adenylate cyclase systemen_US
dc.typeArticleen_US
dc.identifier.emailLin, MC:mcllin@hkucc.hku.hken_US
dc.identifier.authorityLin, MC=rp00746en_US
dc.description.naturelink_to_OA_fulltexten_US
dc.identifier.pmid4358641-
dc.identifier.scopuseid_2-s2.0-0015975817en_US
dc.identifier.volume249en_US
dc.identifier.issue1en_US
dc.identifier.spage59en_US
dc.identifier.epage65en_US
dc.identifier.isiWOS:A1974R800000007-
dc.publisher.placeUnited Statesen_US
dc.identifier.scopusauthoridRodbell, M=7006658086en_US
dc.identifier.scopusauthoridLin, MC=7404816359en_US
dc.identifier.scopusauthoridSalomon, Y=7006956498en_US

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