ATP/ADP BINDING-SITES ARE PRESENT IN THE SULFONYLUREA BINDING-PROTEIN ASSOCIATED WITH BRAIN ATP-SENSITIVE K+ CHANNELS

Covalent labeling of nucleotide binding sites of the purified sulfonylurea receptor has been carried out with alpha-P-32-labeled oxidized ATP. The main part of P-32 incorporation is in the 145-kDa glycoprotein that has been previously shown to be the sulfonylurea binding protein (Bernardi et al., 1988). ATP and ADP protect against this covalent labeling with K0.5 values of 100-mu-M and 500-mu-M, respectively. Non-hydrolyzable analogs of ATP also inhibit P-32 incorporation. Interactions between nucleotide binding sites and sulfonylurea binding sites have then been observed. AMP-PNP, a nonhydrolyzable analog of ATP, produces a small inhibition of [H-3]glibenclamide binding (20-25%) which was not influenced by Mg2+. Conversely, ADP, which also produced a small inhibition (20%) in the absence of Mg2+, produced a large inhibition (approximately 80%) in the presence of Mg2+. This inhibitory effect of the ADP-Mg2+ complex was observed with a K0.5 value of 100 +/- 40-mu-M. All the results taken together indicate that ATP and ADP-Mg2+ binding sites that control the activity of K(ATP) channels are both present on the same subunit that bears the receptors for antidiabetic sulfonylureas.