Characterization of Na+/K+-ATPase from Xenopus laevis kidney. Preliminary results

In Xenopus laevis, the renal Na+/K+-dependent ATPase is a very important enzyme involved in osmoregulatory processes and active transport. The enzyme was obtained from a microsome fraction purified by sucrose discontinuous gradient (10%, 15%, 29.4%) ultracentrifugation after SDS treatment, and concentrated in the denser layer. The assayed biochemical parameters and their values are: 1) Km (ATP): 0.24 mM; 2) K1/2 (Na+): 20.6 mM; 3) K1/2 (K+) 1.6 mM; 4) Ki (ouabain): 0.025 micrometer; 5) optimum pH: 7.2; 6) optimum temperature:" two peaks at 37 degrees C and 45 degrees C.