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  • Title: [Kinetics of the interaction of ATPase of submitochondrial fragments and a natural protein-inhibitor].
    Author: Panchenko MV, Vinogradov AD.
    Journal: Biokhimiia; 1989 Apr; 54(4):569-79. PubMed ID: 2527066.
    Abstract:
    Conditions were selected which enable a quantitative assay of the ATPase inhibitor protein in submitochondrial particles. It was found that the isolated soluble inhibitor exhibits a marked pH-dependent hysteretic behaviour, i. e., an instant jump of pH for the inhibitor solution from 4.8 to 8.2 induced a slow alteration of its activity as measured by the inhibition of ATP hydrolysis by submitochondrial particles. In acid media (pH less than 6.8), the inhibitor is in the active, whereas in alkaline media (pH greater than 6.8) in the inactive state; the apparent pKa value for the cooperative active/inactive transition is 6.8. Treatment of the inhibitor protein with diethylpyrocarbonate, a specific reagent for histidine, completely abolishes its inhibitory activity. Two types of the inhibitor protein--ATPase interaction were revealed, i.e., reversible (ATP-independent) and irreversible (ATP-dependent) ones. Both reactions, i.e., ATP hydrolysis and ATP inhibition by the inhibitor in the presence of Mg2+ are characterized by a hyperbolic dependence of the reaction rate on ATP concentration; however, for both reactions the apparent KmATP values (50 and 5 microM, respectively) differ significantly (pH 8.0). Thus, the inhibitor--ATPase interaction shows that there exists a specific site for ATP in the ATPase which is different from the catalytic one. A model for the inhibitor protein interaction with ATPase which takes account of a slow pH-dependent conformational transformation of the inhibitor protein is proposed.
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