The E1 conformation of Na+/K+ ATPase has:
Post-Albers scheme for P-type ATPases defines two principal conformers interconverting via phosphorylation. E1 state is outward closed, inward open, with N domain positioned to accept ATP and transmembrane domain exposing high affinity sodium sites to cytosol. Detailed structures from shark rectal gland enzyme show three sodium ions coordinated by oxygen atoms in pocket formed by M4, M5, M6 and M8 with micromolar affinity at cytosolic concentration about 10 millimolar, while potassium affinity submillimolar low because pocket incompatible with potassium dehydration geometry. Phosphorylation produces E1P occluded trapping ions, then isomerizes to E2P outward open releasing sodium due to affinity drop thousand fold. In E2, potassium binding sites with different carbonyl arrangement display high potassium affinity from extracellular side where potassium about 4 millimolar, sodium affinity negligible. Dephosphorylation triggers occlusion and transition back to E1. This reciprocal affinity switch ensures ordered antiport. Thus characteristic of E1 conformation is high affinity for sodium and low affinity for potassium as opposed to E2.
Ref: Albers and Post Model, P-Type Pump Cycle, E1 High Na+ Affinity and E2 High K+ Affinity States.