Fig. 2. The catalytic cycle of the gastric H+, K+-ATPase. A hydronium ion binds to the cytoplasmic surface of the gastric H+, K+-ATPase (E1 form) and ATP phosphorylates the protein at Asp386 to form the first ion transport intermediate in the E1P form. The E1P form then converts by a conformational change to the second ion transport form, E2P, with the ion site now exposed to the exterior and hydronium is released. To this form, K+ binds from the outside surface to the same region from which the hydronium was released, and the enzyme dephosphorylates, and then K+ is trapped within the membrane domain in the occluded form. The K+ is then de-occluded allowing reformation of the E1 form of the enzyme with the ion site now again facing the cytoplasm and K+ is displaced when ATP is bound.
© J Neurogastroenterol Motil
