The highly acidic environment in the stomach is essential for digestion. Furthermore, it acts as an important barrier to invasive pathogens. However, excessive stomach acidification leads to ulcers. Although this is not a life-threatening condition, it can considerably impair the health of affected individuals. Acid suppression in combination with antibiotics is the recognized treatment to eradicate the bacteria Helicobacter pylori, a risk factor for gastric cancer. This environment of pH1 is regulated by the gastric H+, K+-ATPase, a class of enzymes that catalyze H+ transport from neutral cytosolic solution (pH 7) to the acidic gastric lumen (pH 1) fueled by cellular energy source ATP. Hence, gastric H+, K+-ATPase are prominent target for drugs that treat excess stomach acid secretion.