Nicotinic acetylcholine receptor protein has been purified from foetal and adult skeletal muscle by extraction in nonionic detergent followed by purification on immobilised a-toxin. Purified foetal and adult receptors focussed as single, sharp peaks whether directly labelled with 125I or indirectly labelled 125I-alpha-bungarotoxin. Polyacrylamide gel electrophoresis of the purified foetal and adult receptors each showed four major protein bands with Mr 44,000, 51,000, 58,000 and 66,000; only that with Mr 44,000 was, in each case, labelled with the affinity reagent, 4-(N-maleimido) [3H] benzyltrimethylammonium. When the four major subunits, obtained by polyacrylamide gel electrophoresis, were labelled with 125I-concanavalin A, markedly different patterns of radioactivity were shown by the foetal and adult receptors, the band at 44,000 being less heavily labelled in the foetal case. Foetal and adult receptors behaved similarly with respect to inhibition by concanavalin 125 A of binding of 125I-alpha-bungarotoxin inhibition in both cases reaching a maximum of 70%. Foetal and adult receptors each showed single 125I-alpha-bungarotoxin binding species in sucrose density gradient centrifugation with s20,w = 8.5S and 9.5s respectively although the former peak was broader, possibly reflecting the relative instability of the purified foetal receptor. The kinetic constants of binding of 125I-alpha-BGT to detergent extracts of adult and foetal muscle were similar and the two receptor types could not be distinguished on this basis.
|Date of Award||1984|