Kinase experiment:

[3H]Soraprazan binding studies are carried out at 20℃. In saturation experiments to determine the Kd value, ion-leaky gastric vesicles (0.01-0.02 mg/mL) are resuspended in a buffer composed of 20 mM Tris-HCl, pH 7.0, 2 mM MgCl2, and 2 mM ATP (pH 7.0 by Tris) in the presence of increasing concentrations of [3H]soraprazan (0.1 nM-1 μM). Nonspecific binding is determined in the presence of a 100 fold excess of unlabeled soraprazan over the concentration range of [3H]soraprazan used. The enzyme suspension (1 mL) is incubated at 20℃ for 30 min and rapidly filtered through a nitrocellulose membrane filter (0.45 μM) prewet with a solution composed of 20 mM Tris-HCl, pH 7.0, 10% polyethylene glycol 3350 that is placed on top of a glass fiber filter. The membrane is ished five times with 2.5 mL of a buffer composed of 20 mM Tris-HCl, pH 7.0, and 10% polyethylene glycol 3350 to remove unbound inhibitor. The membrane is put into a 20-mL scintillation vial, dimethylacetamide (0.5 mL) is added to dissolve the membrane, and 14 mL of scintillation solvent is added and counted. Binding of [3H]soraprazan is determined by subtracting the nonspecific binding of [3H]soraprazan, obtained in the presence of the 100-fold excess of nonradioactive soraprazan, from the amounts of [3H]soraprazan bound to the membrane in the absence of the cold inhibitor.

Soraprazan is a reversible, and fast-acting inhibitor of gastric H+/K+ ATPase.

Soraprazan is a potent inhibitor of gastric H,K-ATPase, with an IC50 of 0.1 μM when measured in ion-leaky vesicles in the presence of 1 mM potassium. Soraprazan also effectively inhibits dibutyryl cAMP-stimulated [14C]AP accumulation in isolated gastric glands with an IC50 of 0.19 μM (0.09-0.40 μM geometric mean from n=6 with 95% confidence limits). In ion-leaky vesicles, soraprazan is a potent k-competitive inhibitor of the H,K-ATPase, with Ki of 6.4 nM. Soraprazan binds to the H,K-ATPase in ion-leaky vesicles with a Kd of 26.4 nM and a Bmax of 2.89 nmol/mg[1].

[1]. Simon WA, et al. Soraprazan: setting new standards in inhibition of gastric acid secretion. J Pharmacol Exp Ther. 2007 Jun;321(3):866-74. Epub 2007 Mar 16.