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  • Title: Calorimetric studies of the interaction of magnesium and phosphate with Na+, K+) ATPase: evidence for a ligand-induced conformational change in the enzyme.
    Author: Kuriki Y, Halsey J, Biltonen R, Racker E.
    Journal: Biochemistry; 1976 Nov 16; 15(23):4956-61. PubMed ID: 136270.
    Abstract:
    The phosphorylation of (Na+, K+)ATPase from the electric organ of the electric eel is dependent on Mg2+. The amount of phosphoenzyme formed was increased by K+ and decreased by Na+. Kinetic analyses indicate that a ternary complex of ATPase, Pi and Mg2+ is formed prior to phosphorylation of the protein. Calorimetric studies revealed extraordinarily large enthalpy changes associated with the binding of Mg2+ (-49 kcal/mol) and of Pi (-42 kcal/mol), indicating a thermodynamically significant conformational change in the enzyme. The dissociation constant for the binding of Mg2+ and Pi derived from calorimetric measurements is in good agreement with the value obtained from the kinetic studies. These results indicate that ion binding induces a conformational change in the enzyme which is a prerequisite for phosphorylation by Pi.
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