FIGURE 3.

Coordination of MgF₄²⁻, a P_i analog, and of a Mg²⁺ ion at the phosphorylation site in the crystal structure of Na,K-ATPase from shark rectal gland in a state representing E2·2K⁺·P_i. In this state the P_i analog MgF₄²⁻ is coordinated by residues in the phosphorylation (P) domain, including the phosphorylated residue D376. A divalent metal ion, in this case Mg²⁺ is located between D376 and another critical residue D717. Orange dotted lines represent coordination of ligands, and green dotted lines show hydrogen bonds likely to be important in stabilizing coordinating residues. Small red spheres represent water molecule. Coordinates of the atomic model are derived from PDB entry 2ZXE.