Effects of carboxymethylation by a purified Torpedo californica methylase on the functional properties of the acetylcholine receptor in reconstituted membranes.
The functional effects of carboxymethylation of Torpedo californica acetylcholine receptor by an endogenous Torpedo methylase were examined. Both the receptor and the methylase were purified to increase the level of methylation and the sensitivity of the functional assays. The methylase catalyzed the carboxymethylation of all four receptor subunits (alpha, beta, gamma, delta) with preferential labeling of the alpha and gamma subunits. For all the reactions, S-adenosylmethionine was used as the methyl donor. Functional effects of methylation were assessed by measuring ligand binding and ligand-activated ion permeability responses in reconstituted membranes containing purified acetylcholine receptors. Methylation of receptor to a level of 20 mol% had no significant effect on agonist or antagonist binding nor did methylation affect the transition from low-to-high affinity binding triggered by agonists. In contrast, 20% methylation led to a 20% reduction in the agonist-stimulated flux of cations across the receptor-containing membranes. The results suggest that methylation inhibits the ion permeability control properties of acetylcholine receptors.
A S
AS
Yee
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MG
McNamee
D000818:Animals; D002384:Catalysis; D002463:Cell Membrane Permeability; D004557:Electric Organ / Q000201:enzymology; D066298:In Vitro Techniques; D007473:Ion Channels / Q000378:metabolism; D008024:Ligands; D008745:Methylation; D008780:Methyltransferases / Q000302:isolation & purification / Q000378:metabolism*; D011950:Receptors, Cholinergic / Q000378:metabolism*; D012995:Solubility; D014101:Torpedo
D007473:Ion Channels; D008024:Ligands; D011950:Receptors, Cholinergic; D008780:Methyltransferases