The K+-dependent phosphatase from human renal tissue: its properties and time dependent inhibition by ouabain.

The K+-dependent p-nitrophenyl phosphatase activity associated with human renal (Na+ + K+)-ATPase was examined for some of its kinetic properties. ATP inhibited the K+-dependent phosphatase and raised the Km for p-nitrophenylphosphate. Stimulation of the K+-dependent phosphatase by K+ was blocked by Na+ in a noncompetitive manner. Inhibition of the K+-dependent phosphatase by ouabain was dependent upon incubation time. The apparent Kï was 2.0 micron.