The H+/ATP stoichiometry of the (H+ +K+)-ATPase of dog gastric microsomes.
Gastric microsomal vesicles isolated from dog fundic mucosa were shown to be relatively ion tight and have a low level of proton permeability. The H+ translocase, basal ATPase and K+-activated ATPase activities of these vesicles were measured and the H+/ATP stoichiometry calculated using either the total K+-ATPase or the K+-stimulatable component (total K+-ATPase--basal ATPase). The former estimations consistently gave stoichiometric of approximately one, whereas the use of only the K+-stimulatable component gave widely differing values. Measurement of the dephosphorylation of the enzyme under basal conditions revealed both a labile and a stable phosphoenzyme component. The rate of decay of the labile component completely accounted for the basal ATPase activity observed. We conclude that the basal ATPase associated with our preparations is a spontaneous dephosphorylation of the phosphoenzyme occurring in the absence of K+ and that the H+/ATP stoichiometry of the gastric ATPase is one.
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D004285:Dogs; D005753:Gastric Mucosa / Q000201:enzymology; D017506:H(+)-K(+)-Exchanging ATPase; D007700:Kinetics; D008861:Microsomes / Q000201:enzymology; D011188:Potassium; D011522:Protons; D013270:Stomach / Q000201:enzymology*
D011522:Protons; D000251:Adenosine Triphosphatases; D017506:H(+)-K(+)-Exchanging ATPase; D011188:Potassium