title: The interaction of H+ and K+ with the partial reactions of gastric (H+ + K+)-ATPase.
abstract: The influence of H+ and K+ on the partial reactions and transport of gastric (H+ + K+)-ATPase was studied. Using transient kinetics, the effects and sidedness of effects of H+ and K+ on formation and breakdown of phosphoenzyme were determined in intact and lyophilized reconstituted vesicles in the absence and presence of gramicidin. Whereas increasing H+ concentrations on the ATP-binding face of the vesicles accelerates phosphorylation, increasing K+ concentrations inhibits phosphorylation. Increasing H+ on this side reduces K+ inhibition of the phosphorylation rate. At low ATP/K+ ratios, the phosphorylation step can become rate-limiting for steady state hydrolysis. Decreasing H+ accelerates dephosphorylation in the absence of K+. K+ on the internal or luminal face of the vesicles accelerates dephosphorylation, and this rate is reduced with increasing H+ concentrations. At low internal pH, K+-dependent dephosphorylation may become rate-limiting. H+ transport measurements using fluorescence quenching of acridine orange show that whereas internal K+ is required for H+ transport, external K+ inhibits the rate of formation of a pH gradient, and the inhibition is reduced by decreasing medium pH. The pH optimum for ATPase activity and transport correlated in the vesicles, and the K0.5 of K+ for transport correlated with data for intact parietal cells.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D017506:H(+)-K(+)-Exchanging ATPase; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008433:Mathematics; D010766:Phosphorylation; D011188:Potassium / Q000494:pharmacology; D013270:Stomach / Q000201:enzymology*; D013552:Swine; D014634:Valinomycin / Q000494:pharmacology
chemical_list: D014634:Valinomycin; D000251:Adenosine Triphosphatases; D017506:H(+)-K(+)-Exchanging ATPase; D011188:Potassium