Interaction of Na+, K+, and ATP with Na,K-ATPase

GARRAHAN, P. J.; ROSSI, R. C.; REGA A. F.

CURRENT TOPICS IN MEMBRANES

ELSEVIER ACADEMIC PRESS INC

Lugar: Burlington, MA, Estados Unidos; Año: 1983 vol. 19 p. 561 - 564

1063-5823

Although a great deal of experimental information on the elementary steps of the hydrolysis of ATP catalyzed by the Na, K-ATPase is available, few attempts have been made to see to what extent reaction schemes based on results from experiments on partial reactions are able to predict the steady-state kinetic behavior of the enzyme. This chapter reviews the experiments of the interactions of ATP, a nonhydrolyzable analog of ATP adenylylmethylene diphosphonate (AMPPCP), Na+, and K with the Na, K-ATPase and confronted the results with the predictions of the current schemes for the hydrolysis of ATP by the Na, K?ATPase. Na, K?ATPase was prepared from dog kidney red outer medulla by the simpler of the two procedures described by Jørgensen. ATPase activity was measured by the release of [32P]Pi from [γ-32P]ATP at 37°C and at pH 7.4 and 150 mM total salt concentration. AMPPCP acts as a competitive inhibitor of ATP at the high-affinity component of the substrate curve of the ATPase. The high-affinity component of the substrate curve expresses the combination of ATP at a catalytic site and that the low-affinity component expresses the combination of ATP at a site from which the nucleotide activates the ATPase without undergoing hydrolysis.