The interaction of H+ and K+ with the partial reactions of gastric (H+ + K+)-ATPase

• Published in: The Journal of biological chemistry 1981-03, Vol.256 (6), p.2682-2690
• Main Authors: Stewart, B, Wallmark, B, Sachs, G
• Format: Article
• Language: English
• Subjects: Adenosine Triphosphatases - metabolism; Animals; H(+)-K(+)-Exchanging ATPase; Hydrogen-Ion Concentration; Kinetics; Mathematics; Phosphorylation; Potassium - pharmacology; Stomach - enzymology; Swine; Valinomycin - pharmacology
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(19)69668-7

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.