Abstract
The affinity for agonists, but not for antagonists, is changed by guanine nucleotide in muscarinic ACh receptors (mAChR) as in the other neurotransmitter receptors. Sulfhydryl reagents are also known to change the affinity of mAChR for agonists. Following results were obtained by the radiation inactivation experiment, trypsin treatment and computer analysis of the inhibition curves of 3H-QNB binding by Carbachol: 1)MAChR consists of three subtypes or states which have different affinities for agonists (Super-high(SH), High(H) and Low(L) affinity agonist binding sites). 2)SH was converted to L by guanine nucleotide and inversely L to SH by sulfhydryl reagent, DTNB. 3)SH state of mAChR was attached by another protein (G protein) and guanine nucleotide dissociates G protein from mAChR, causing L state. 4)DTNB seems to act directly on mAChR, causing SH state.
Published Version
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