Na⁺/K⁺-ATPase: Regulation of K⁺ Access Channels by K⁺

Abstract

Based on studies with the purified canine kidney enzyme (1), we concluded recently that Rb⁺ (or K⁺) occlusion sites of the unphosphorylated E₂ state of the enzyme are confined within the protein matrix and connected to the medium by narrow and heterogeneous access channels, and that channel heterogeneity is distinct from any differences that may exist among the affinities of the occluded sites that are deep within these channels. More importantly, the same studies indicated that regulation of these channels is also distinct from the regulation of the events at the occluded sites, and identified allosteric regulatory effects of ATP, Na⁺, and Rb⁺ on the “width” of the access channels. Here, we present further findings on the interactive allosteric effects of ATP and Rb⁺ (or K⁺) on these channels. All experiments were done at 4±C by methods and procedures described before (1).