Dynamic properties of isolated acetylcholine receptor proteins: release of calcium ions caused by acetylcholine binding.
- 1 October 1976
- journal article
- research article
- Published by Proceedings of the National Academy of Sciences in Proceedings of the National Academy of Sciences
- Vol. 73 (10) , 3364-3368
- https://doi.org/10.1073/pnas.73.10.3364
Abstract
Interaction of Ca2+ and acetylcholine (AcCh) ions with purified acetylcholine receptor (AcChR) from Torpedo californica and Electrophorus electricus was investigated in view of these ions'' role proposed in bioelectricity. Spectrophotometric Ca2+ titration using murexide as an indicator and an ultrafiltration method with 45Ca show that AcChR proteins have a high binding capacity for Ca2+. Per macromolecule of 260,000 daltons, up to 60 Ca2+ were bound with at least 3 Ca2+ dissociation constants. A linear inhibition of AcCh binding to AcChR by Ca2+ was observed in the 0.1-1 mM Ca2+ range, indicating competition of AcCh and Ca2+ for AcChR. The addition of AcCh to a Ca2+-AcChR solution at 1.2 mM Ca2+ caused release of 4-6 bound Ca2+ ions from AcChR when a maximum of 2 AcCh ions were bound per 260,000 dalton macromolecule. The subsequent addition of .alpha.-bungarotoxin causes reuptake of up to 6 Ca2+ ions by AcChR. The neural activator AcCh and the inhibitor .alpha.-bungarotoxin may induce opposing shifts between different conformational states of isolated AcChR.This publication has 17 references indexed in Scilit:
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