Gastric (H+,K+)-ATPase.
Gastric acid secretion results from the activity of a specific ATPase, the (H+,K+)-ATPase. This enzyme, discovered in 1973, exchanges H+ for K+. It has two ATP binding sites, both involved in enzyme activity, whose affinities vary as a function of the H+ and K+ concentrations. Hydrolysis of ATP at the highest affinity site leads to the synthesis of a covalent aspartyl phosphate which accumulates in the absence of K+. The presence of this cation accelerates dephosphorylation resulting in the stimulation of ATPase (and PNPPase) activity. The structure of membranous (H+,K+)-ATPase is poorly defined. n-Octylglucoside solubilizes an active enzyme of 390-420 kDa which can be partly depolymerized using cholate. The monomer, characterized in SDS has a 95 kDa molecular mass and is inactive. In the presence of magnesium, (H+,K+)-ATPase catalyzes the active and neutral exchange of H+ for K+ at the expense of ATP. In the absence of ATP, (H+,K+)-ATPase acts as a passive transporter exchanging K+ for K+ at maximal rate and H+ for K+ at a 20 times slower rate.
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D001692:Biological Transport; D005750:Gastric Juice / Q000378:metabolism*; D005753:Gastric Mucosa / Q000201:enzymology*; D017506:H(+)-K(+)-Exchanging ATPase; D006801:Humans; D046911:Macromolecular Substances; D008565:Membrane Proteins / Q000378:metabolism
D046911:Macromolecular Substances; D008565:Membrane Proteins; D000251:Adenosine Triphosphatases; D017506:H(+)-K(+)-Exchanging ATPase