The TVGYG motif was discovered in a Streptomyces A protein that binds this ion. Proton pumps in the stomach exchange hydrogen for this ion. Transport of this ion through a ball-and-chain voltage-gated channel is impaired in Shaker mice. This ion has the highest permeability, concentration, and mass of the three species in the Goldman (0[1])equation. (20[1])Diuretics like amiloride “spare” the excretion of this primary (0[1])intracellular (*) electrolyte to prevent hypokalemia. This ion floods out of a cell during hyperpolarization, then is pumped back in, two at a time, after the action potential is over. Three-quarters of a neuron’s ATP is used to exchange this ion for sodium. (10[1])For 10 points, name this elemental ion found naturally in bananas. ■END■ (10[2])