Intra α subunit distance changes upon ouabain binding to the Na+/K+-ATPase. (a) Sensitized emissions of the pump construct 324LBT(αM3–M4)-S886C(αM7)/βWT. In the absence of ouabain, sensitized emission decayed with a τSE of 1.45 ms (black trace). Ouabain bound to these pumps slowed down the sensitized emission decay to 1.69 ms (gray trace). (b) Sensitized emissions of the pump construct 125LBT(αM1–M2)-I810C(αM6)/βWT. In this example, ouabain binding accelerated τSE from 1.30 (black trace; absence) to 1.12 ms (gray trace; presence). (c) Distance estimations. Distance estimated for all intra α subunit constructs tested: 125LBT(αM1–M2)-L800C(αM5)/βWT (n=7), 125LBT(αM1–M2)-I810C(αM6)/βWT (15), 324LBT(αM3–M4)-S886C(αM7)/βWT (n=7), 988LBT(αM9–M10)-S886C(αM7)/βWT (n=4) and 988LBT(αM9–M10)-I810C(αM6)/βWT (n=5). Black bars correspond to distances without ouabain while gray bars represent distances upon ouabain binding. Upper bars show the Δ distances produced by ouabain binding.