Comparison of the kinetic properties of membrane-bound and solubilized Na,K-ATPase.

Substrate-velocity curve for Na,K-ATPase under optimal conditions is described as a curve with intermediary plateau. C12E2 treatment of the enzyme changes its kinetic behaviour. The substrate-velocity curve transforms into hyperbolic one and the Km value for the solubilized enzyme approaches the Km value for the first phase of the complex curve. The experimental substrate-velocity curves obtained for Na,K-ATPase under different conditions were analyzed on the basis of the sum of Michaelis and Hill equations and the kinetic scheme for the enzyme was proposed. This model suggests that at the definite step of the reaction cycle the short-living oligomer is formed which can bind ATP with higher affinity thus accelerating E2----E1 transition. Several additional experimental facts that prove the hypothesis are presented.