Journal ArticleDOI
The regulatory control of beta-receptor dependent adenylate cyclase.
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TLDR
The characteristics of the β-receptor in turkey erythrocyte adenylate cyclase were studied and it was found that the role of the catecholamine hormone is to facilitate the activation of the enzyme by the guanyl nucleotide.Abstract:
The characteristics of the β-receptor in turkey erythrocyte adenylate cyclase were studied using both kinetics of enzyme activation and direct binding measurement of the β-agonists and antagonists to the β-receptor. The regulatory ligands Gpp(NH)p and Ca2+ do not have any direct effect on the β-receptor, but modulate the enzyme activity through the interaction with specific regulatory sites.
It was found that the role of the catecholamine hormone is to facilitate the activation of the enzyme by the guanyl nucleotide. The regulatory guanyl nucleotide binds to its allosteric site in the absence of hormone, but the activation of the enzyme is slow in the absence of hormone. This role of the hormone can be described by the scheme:
Where R is the receptor, E the enzyme, G the guanyl nucleotide, H the hormone, and E′ the activated form of the enzyme. The binding steps are fast and reversible but the conversion of the inactive enzyme E to its active form occurs with a k∼1.0 min−1 In the absence of the β-agonist (l-catecholamine) at the β-receptor and at physiological free Mg2+ concentrations, the activation of the enzyme is insignificant. Thus the presence of a guanyl nucleotide at the allosteric site is obligatory but not sufficient to induce the conversion of the inactive enzyme to its active form. At high (nonphysiological) Mg2+ concentration the conversion of E to E′ occurs slowly in the absence of hormone probably by another pathway.
There are two classes of Gpp(NH)p regulatory sites: tight sites and loose sites, both of which can be identified kinetically. We have also identified the tight sites by direct binding studies using 3H-Gpp(NH)p. It is not clear, however, whether these are two distinct classes of sites or whether their existence reflects the presence of negative cooperativity among the guanyl nucleotide regulatory sites.
Calcium was found to be a negative allosteric inhibitor of adenylate cyclase. The inhibitory effect of Ca2+ is exerted on the nonactivated enzyme as well as on the Gpp(NH)p preactivated enzyme.read more
Citations
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Journal ArticleDOI
Mode of coupling between the beta-adrenergic receptor and adenylate cyclase in turkey erythrocytes.
TL;DR: The data strongly suggest that the collision coupling is the mode of coupling between the beta receptor and cyclase coupling in turkey erythrocyte membranes.
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Slowly reversible binding of catecholamine to a nucleotide-sensitive state of the beta-adrenergic receptor.
L T Williams,R J Lefkowitz +1 more
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Differential Regulation by Guanine Nucleotides of Opiate Agonist and Antagonist Receptor Interactions
TL;DR: By affecting binding of agonists, but not antagonists, GTP may regulate opiate receptor interactions with their physiological effectors.
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Selective Binding Site for [3H]Prostacyclin on Platelets
TL;DR: The higher affinity binding site for PGI(2) appears to be the specific receptor through which PGI (2) exerts its effect on platelets.
References
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Journal ArticleDOI
The Glucagon-sensitive Adenyl Cyclase System in Plasma Membranes of Rat Liver V. AN OBLIGATORY ROLE OF GUANYL NUCLEOTIDES IN GLUCAGON ACTION
TL;DR: It is concluded that guanyl nucleotides play a specific and obligatory role in the activation of adenyl cyclase by glucagon, and bind at sites, distinct from the glucagon binding sites, that appear to regulate both the response ofadenyl cycling to glucagon and the actions of fluoride ion on this system.
Journal ArticleDOI
The glucagon-sensitive adenyl cyclase system in plasma membranes of rat liver. IV. Effects of guanylnucleotides on binding of 125I-glucagon.
TL;DR: In this article, the effects of nucleotides on binding of 125I-glucagon at specific binding sites in plasma membranes of rat liver GTP and GDP, equally and at a minimal concentration of 005 µm, stimulate the rate and degree of dissociation of bound labeled hormone, decrease uptake of glucagon by the membranes, and decrease the affinity of the binding sites for glucagon.
Journal ArticleDOI
Negative cooperativity in regulatory enzymes
TL;DR: Findings in CTP synthetase add strong support for the sequential model of subunit interactions which postulates that ligand-induced conformational changes are responsible for regulatory and cooperative phenomena in enzymes.
Journal ArticleDOI
Activation of pigeon erythrocyte membrane adenylate cyclase by guanylnucleotide analogues and separation of a nucleotide binding protein.
T Pfeuffer,E J Helmreich +1 more
TL;DR: It is assumed that the GTP analogues cause an unphysiological, irreversible activation of membrane-bound adenylate cyclase, because, in contrast to the natural guanylnucleotides whose action they mimic, they are metabolically inert and bound quasi-irreversibly to regulatory sites.
Journal ArticleDOI
5′-Guanylylimidodiphosphate, A Potent Activator of Adenylate Cyclase Systems in Eukaryotic Cells
Constantine Londos,Yoram Salomon,Michael C. Lin,James P. Harwood,Michael Schramm,J. Wolff,Martin Rodbell +6 more
TL;DR: Gpp(NH)p appears to be a useful probe for investigating the mechanism of hormone and nucleotide action on adenylate cyclase systems in eukaryotic cells.
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