Figure 1.

(A) Albers-Post scheme for the Na⁺/K⁺ ATPase reaction cycle. (B) Scheme of the experimental setup used for voltage-clamp fluorometry. (C) Schematic diagram of the transmembrane domain and adjacent residues of the sheep β1 subunit of the Na⁺/K⁺-ATPase. The diagram depicts residues Arg-27 to Ala-73; in bold are shown the 11 residues Met-57 to Tyr-67, which were individually replaced by cysteines for the purpose of site-directed fluorescence labeling. Three residues that demonstrate significant fluorescence changes in response to voltage pulses are colored red.