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. 1989 Jan 15;257(2):611-4.
doi: 10.1042/bj2570611.

Essential Role of Magnesium in Oxytocin-Receptor Affinity and Ligand Specificity

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Free PMC article

Essential Role of Magnesium in Oxytocin-Receptor Affinity and Ligand Specificity

F A Antoni et al. Biochem J. .
Free PMC article

Abstract

We have analysed, with the aid of a novel radioiodinated oxytocin (OT)-receptor antagonist, the role of Mg2+ in uterine OT-receptor function. The antagonist-receptor interaction was characterized by high affinity, reversibility and stereospecificity in Tris/HCl buffer containing 3 mmol of Mg2+/litre as well as buffer free of Mg2+. By contrast, omission of Mg2+ decreased the affinity of the receptor for OT by about 1500-fold; moreover, the stereospecificity of agonist, but not antagonist, binding was lost. Since guanine nucleotides had relatively minor effects in this system (less than or equal to 2-fold decrease in OT affinity), we suggest that the agonist-binding site of OT receptors is directly modulated by Mg2+, unlike other receptors, where the effects of bivalent cations are exerted via guanine-nucleotide-binding (G-) proteins. Thus the ligand recognition mechanism of OT receptors may be novel in this respect.

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