TY - JOUR T1 - The binding properties of the solubilized sulfonylurea receptor from a pancreatic B-cell line are modulated by the Mg(++)-complex of ATP. JF - Journal of Pharmacology and Experimental Therapeutics JO - J Pharmacol Exp Ther SP - 495 LP - 502 VL - 262 IS - 2 AU - M Schwanstecher AU - S Behrends AU - C Brandt AU - U Panten Y1 - 1992/08/01 UR - http://jpet.aspetjournals.org/content/262/2/495.abstract N2 - Previous studies demonstrated that the Mg complex of ATP decreases glyburide- and increases diazoxide-binding to membranes from pancreatic islets. To examine further the mechanism of these effects, the sulfonylurea receptors in microsomes of the hamster B-cell line HIT-T15 were solubilized with detergents. Maximum recovery of receptors (40%) was obtained with Triton X-100. Specific binding of [3H]glyburide to the solubilized receptors (Kd = 0.35 nM, maximum number of binding sites = 170 fmol/mg of protein) corresponded well to specific binding to microsomes. In Triton X-100 extracts, MgATP (300 microM) reduced the number of high-affinity sites for [3H]glyburide by 50% and increased the dissociation constant for [3H]glyburide by 4-fold; MgATP was half-maximally effective at 20 microM. Development of MgATP-induced inhibition of [3H]glyburide binding to solubilized binding sites was not slower than dissociation of [3H]glyburide binding. Alkaline phosphatase accelerated the reversal of MgATP-induced inhibition of [3H]glyburide binding. In the presence of Mg++, not only ATP but also ADP, GTP and GDP inhibited [3H]glyburide binding to the solubilized receptor. However, MgADP did not inhibit [3H]glyburide binding when the MgATP concentration was kept low by the hexokinase reaction. MgATP significantly enhanced diazoxide-induced displacement of [3H]glyburide from the solubilized receptor. The MgATP-induced inhibition of binding was weakened by millimolar concentrations of free ATP. It is concluded that the binding sites for MgATP, glyburide and diazoxide are located at a single protein or at closely associated proteins which may include a protein kinase. ER -