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J M Stockton

Publications and source records attributed to J M Stockton.

11 recordsLinked to original sources
PubMed1987

Muscarinic acetylcholine receptors: structure, function subtypes and therapeutic perspectives.

Structural and binding studies on the purified rat forebrain muscarinic acetylcholine receptor (mAChR) are consistent with the idea that the receptor is structurally analogous to rhodopsin. We propose that it consists of a short, glycosylated N-terminus, followed by seven transmembrane helices, joined by extra-membranous loops. The transmembrane helices make up a substantial proportion of the molecule. Two peptides, one of which is glycosylated, and therefore close to the N-terminal part of the molecule are labelled on acidic residues by the irreversible antagonist, [3H]-PrBCM, and may thus form part of the ligand binding site. The conformational flexibility of the mAChR, and hence its ability to bind rigid selective ligands such as pirenzepine is strongly affected by the oxidation state of key cysteine residues. The molecule is proposed to terminate in a cytoplasmic C-terminal tail, which participates, together with the cytoplasmic loops, in the recognition of GTP-binding proteins. The C-terminus is susceptible to proteolytic attack, and shows evidence of sequence homology to the C-terminus of the beta-adrenergic receptor.

Animals↗
PubMed1986

Soluble and membrane-bound muscarinic acetylcholine receptors.

Three muscarinic acetylcholine receptor subtypes may be defined on the basis of functional and binding studies using selective antagonists. The subtypes may be solubilized in a stable form in digitonin. In solution, the subclasses still exhibit different structure-binding relationships but these have been perturbed by solubilization. The binding of the selective antagonist, pirenzepine, to the purified cortical receptor is complex and similar to that found in membranes. The muscarinic receptor subclasses thus appear to be different molecular entities. Possible explanations for the molecular heterogeneity are discussed. It has also been possible to solubilize receptor-GTP binding protein complexes which have higher sedimentation coefficients (13.4 S) than the apparently monomeric receptor (11.6 S).

Animals↗
PubMed1985

Solubilization and characterization of high and low affinity pirenzepine binding sites from rat cerebral cortex.

An apparently monomeric form of the digitonin-solubilized muscarinic acetylcholine receptor from the rat cerebral cortex retains a high affinity of 7 X 10(7) M-1 for pirenzepine. Muscarinic receptor binding sites in the rat cerebral cortex with a low affinity for pirenzepine are solubilized with relatively little change in affinity. The ability of pirenzepine to distinguish between subtypes of muscarinic binding site in the cerebral cortex is manifest in both the membrane-bound and soluble state.

Animals↗
PubMed1984

Solubilization and characterization of guanine nucleotide-sensitive muscarinic agonist binding sites from rat myocardium.

Muscarinic receptors from rat myocardial membranes may be solubilized by digitonin in good yield at low temperatures in the presence of Mg2+. Under these conditions, up to 60% of the soluble receptors show high affinity binding for the potent agonist [3H]-oxotremorine-M (KA = 10(9)M-1), which is inhibited by 5'-guanylylimidodiphosphate. The muscarinic binding site labelled with [3H]-oxotremorine-M has a higher sedimentation coefficient (13.4 s) than sites labelled with a 3H antagonist in the presence of guanylylimidodiphosphate (11.6 s) and probably represents a complex between the ligand binding subunit of the receptor and a guanine nucleotide binding protein.

Animals↗
PubMed1983

Regulation of muscarinic agonist binding by cations and guanine nucleotides.

EDTA treatment of membrane preparations from rat brain and myocardium reduced the relative proportion of superhigh and high affinity binding sites for muscarinic agonists by up to 60%. This effect was partially or completely reversed by millimolar concentrations of Mg2+ or Mn2+. A number of multivalent metal cations gave qualitatively similar effects, yielding stimulation of agonist binding at low concentrations but inhibition at higher concentrations. The divalent cation-linked subpopulation of muscarinic agonist binding sites identified in this study appears to be the primary target for guanine nucleotide inhibition.

Animals↗
PubMed1983

Modification of the binding properties of muscarinic receptors by gallamine.

The interaction of gallamine with muscarinic receptors from different tissues has been investigated. Gallamine binds to a site distinct from the conventional muscarinic ligand binding site and modulates the binding of agonists and antagonists to the conventional binding site. In agreement with reported pharmacological studies, the effects of gallamine on the binding of muscarinic ligands are much greater in heart than in other tissues. These findings suggest the possibility of developing novel and selective muscarinic drugs.

Animals↗
PubMed1981

Characterization of adenylate cyclase purified from rat brain by hydrophobic chromatography.

Hydrophobic chromatography of detergent-solubilized rat brain adenylate cyclase on dodecyl-Sepharose produced a species that was soluble in the absence of detergent and could be manipulated like a conventional hydrophilic protein. Sevenfold purification was achieved by this technique. Further purification could then be effected by affinity chromatography on ATP-Sepharose. The purified enzyme was no longer sensitive to fluoride or guanyl nucleotides. No interaction of brain adenylate cyclase was observed with immobilized triazinyl dyes such as Cibacron Blue 3GA nor with con-canavalin A-Sepharose. The molecular weight of the fluoride-activated catalytic complex in a freeze-dried membrane preparation was estimated to be 133,000 by irradiation inactivation.

Adenylyl Cyclases↗