Studies on specific properties of dog heart (Na+-K+)-ATPase

Three different methods used for partial purification of (Na+-K+)-ATPase, Method a, Matsui and Schwartz (5), Method b, Fedelesová et al. (3), and Method c, Pitts et al. (6), were compared with respect to specific activities, yields, and recovery of the enzyme in preparations from the dog heart. Highest specific activities of (Na++K+)-ATPase, as well as the ratio of (Na+, +K+) + Mg2+ to Mg2+-ATPase, and the second best recovery and yield have been found in the preparation obtained by Method b. However, using Method c, which includes two deoxycholate treatments no high (Na++K+)-ATPase activity could be obtained after the second treatment although the yields of protein did not differ from those reported by Pitts et al. (6). Therefore, the other specific properties of the dog heart (Na++K+)-ATPase were compared only in enzyme obtained by Lubrol extraction (Method b) and after NaI treatment (Method a). The Na+ to K+ concentration ratio necessary for optimal stimulation of (Na++K+)-ATPase activity as well as the pH optimum of the enzyme proved to be similar in NaI- and Lubrol-treated preparations, whereas in the latter the sensitivity to ouabain was 4.55 times higher than in NaI-treated preparation. The Km values for MgATP2-, Kh values for Na+ and K+ activation, and S50 values for Na+ activation were similar in preparations obtained by Methods a and b, whereas the values of (n) for K+ and Na+ activation and S50 for K+ activation were slightly higher in the NaI-treated fraction.