论文信息 - Relationship between Ouabain‐Sensitive ATPase Activity and Occluded Rb+ at Micromolar ATP Concentrations a

Relationship between Ouabain‐Sensitive ATPase Activity and Occluded Rb+ at Micromolar ATP Concentrations a

This communication describes an attempt to evaluate the obligatory role of the intermediate with occluded potassium, E?(K?), during K + transport by the Nat/K+ATPase. Using 86Rb to measure the occluded form at steady state and [ATP] from 0.5-10 pM, we found that when [Rb’] 5 10 mM, only part of the Na+/K+-ATPase activity takes place through the E2(Rb2) and E2(Rb*)ATP forms, so that at these Rb’ concentrations the preparation has “extra” ouabain-inhibitable ATPase activity. The scheme in FIGURE 1 represents the currently accepted model for K+ activation and Kt transport by the Na+/K+-ATPase. Equation 4 (FIG. 1, legend) predicts that at saturating K + concentrations, the ratio ulE,,~ will increase with the concentration of ATP along a rectangular hyperbola. However, under the conditions of this study, [ATP] << KATp, so that v/Eo,,l approaches a linear function of [ATP]:

P. J. Garrahan | P. Schwarzbaum | S. B. Kaufman | R. C. Rossi | J. G. Nørby

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