Yi. Fang et al., PARTIAL-PURIFICATION OF AN ENDOGENOUS INHIBITOR OF MUSCARINIC LIGAND-BINDING, Biochemistry and molecular biology international, 38(3), 1996, pp. 501-507
An endogenous inhibitory factor (EIF alpha) to the binding of a muscar
inic antagonist, [H-3]N-methyl scopolamine ([H-3]NMS), has been partia
lly (12-fold) purified from the soluble fraction of the ileal longitud
inal muscle of guinea-pigs using a heat-treatment, isoelectric fractio
nation, and DEAF-column chromatography. The EIF alpha inhibited the [H
-3]NMS binding to the longitudinal muscle membrane with an IC50 of 53.
6 mu g/ml. This was about 230-fold potent than the non-specific inhibi
tion of [H-3]NMS binding by bovine serum albumin (BSA). Zn2+ (0.1 mM)
almost completely blocked the inhibitory activity of EIF alpha, wherea
s such the effect of Zn2+ was not observed in the inhibition by BSA. T
hese results suggest that EIF alpha inhibits the [H-3]NMS binding to t
he muscarinic acetylcholine receptor in a different manner from non-sp
ecific interaction with the receptor.