title: Terbium binding to rat brain acetylcholinesterase. A fluorescence probe of anionic sites.
abstract: Studies are in progress to characterize the nature of ligand interactions at peripheral anionic sites on mammalian brain AChE, including the beta-anionic or "accelerator" anionic sites where enzyme activity is increased upon Ca2+ binding. Terbium was studied as a fluorescence probe of Ca2+ binding sites in partially purified AChE from whole rat brain. Scatchard analysis of Tb3+ binding in low ionic strength (2 mM) Pipes buffer revealed at least two populations of sites: high affinity sites with Kd(app) approximately 7.6 microM and low-affinity sites with a Kd(app) approximately 49.6 microM. Low-affinity binding was selectively inhibited by 50 mM NaCl; high-affinity binding was completely inhibited by 2 mM CaCl2; and all the bound Tb3+ could be displaced by 1 mM EDTA. The heterogeneity of Tb3+ binding sites is consistent with the multiple, concentration-dependent effects of Tb3+ on enzyme activity.
mesh_terms: D000110:Acetylcholinesterase / Q000378:metabolism*; D000818:Animals; D000838:Anions; D001665:Binding Sites; D001921:Brain / Q000201:enzymology / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D051381:Rats; D013050:Spectrometry, Fluorescence / Q000379:methods; D013725:Terbium / Q000378:metabolism*
chemical_list: D000838:Anions; D013725:Terbium; D000110:Acetylcholinesterase; D002118:Calcium