An automated assay for Na-K ATPase kinetics

We have developed an automated assay for the Na and K activated ATPase which has been used to determine the enzyme activity in a sample of unknown enzymatic activity or the dependence of the initial rate of reaction on ligand concentration where identical samples of enzyme are used. The interference of nucleotides on the color development of the phosphomolybdate complex has been eliminated by the addition of MgCl₂ to the acid molyb-date solution. Ways of handling the microsomal Na and K stimulated ATPase have been found which insure the stability of the enzyme and facilitate washing through autoanalyzer tubing. Finally, a modification of normal autoanalyzer procedures permits kinetic analysis to be carried out in an automated fashion.