The intermediary complexes formed by (Na + + K + )-dependent ATPase.

Abstract

Abstract 1. 1. The microsomal pellet obtained from the isolated mucosal cells of bladders of freshwater turtles contains a (Na+ + K+)-ATPase activity. 2. 2. Mg2+-dependent 32P-labeling of the native and ouabain-trated protein by [γ-32P]ATP at 0° amounts to 0.29 and 0.19 nmole P per mg protein per 50 sec, respectively. In the native protein, addition of Na+ increased this labeling by 158%; and addition of Na+ + K+, decreased the labeling of the protein to the underlying Mg2-dependent level. In the ouabain-treated protein, addition of Na+ increased Mg2+-dependent labeling by 220%; but addition of Na+ + K+ resulted in no change in labeling which remained at the Mg2+ + Na+-dependent level. 3. 3. Mg2+-dependent 14C labeling of the native microsomal protein by [14C]ATP at 0° amounts to 0.72 nmole/mg porotein per 50 sec; and addition of Na+ decreases the Mg2+-dependent labeling by 46%. 4. 4. The Na+-induced decrement in microsomal binding of [14C]ATP simultaneously with the Na+-induced increment in binding of [32P]ATP suggests the formation and breakdown of a Na+-sensitive enzyme-ATP complex.