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The gastric [H,K]ATPase:H+/ATP stoichiometry.

E C Rabon, T L McFall, G Sachs

    The Journal of Biological Chemistry
    |June 10, 1982
    PubMed
    Summary

    The gastric [H,K]ATPase proton pump exhibits an H+/ATP ratio of 2, indicating two protons are transported per ATP molecule. This stoichiometry is consistent across varying potassium and ATP concentrations, crucial for understanding gastric acid secretion.

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    Area of Science:

    • Biochemistry
    • Molecular Biology
    • Physiology

    Background:

    • The gastric [H,K]ATPase is a key enzyme responsible for acid secretion in the stomach.
    • Understanding the stoichiometry of proton (H+) transport is vital for elucidating the enzyme's mechanism.
    • Previous studies have suggested varying H+/ATP ratios, necessitating precise determination.

    Purpose of the Study:

    • To accurately determine the H+/ATP stoichiometry of the purified gastric [H,K]ATPase.
    • To investigate the influence of external potassium (K+) and ATP concentrations on the H+/ATP ratio.
    • To assess the role of ionophores in modulating proton transport.

    Main Methods:

    • Initial rate measurements of H+ transport and K+-stimulated ATPase activity in a purified gastric microsomal fraction.
    • Varying external KCl concentrations (12 to 150 mM) and ATP concentrations.
    • Utilized valinomycin as an ionophore to assess its effect on net H+ transport.

    Main Results:

    • An H+/ATP ratio of 2 was determined for H+ transport at pH 6.1.
    • The H+/ATP ratio remained consistent and independent of external KCl and ATP concentrations.
    • Net H+ transport increased by approximately 29% with the addition of valinomycin.

    Conclusions:

    • The gastric [H,K]ATPase exhibits a fixed H+/ATP stoichiometry of 2, signifying efficient proton translocation per ATP hydrolysis.
    • The enzyme's kinetic parameters (K0.5 for ATP) are significantly modulated by external K+ concentration.
    • The findings provide critical insights into the mechanism of gastric acid production and potential therapeutic targets.

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