3. SODIUM – POTASSIUM PUMP  Inside Cell:  High K + / Low Na + relative to extracellular medium  The sodium potassium pump uses energy to generate and maintain these concentration gradients  Moves Na + out, K + in whilst hydrolysing ATP  Uses up approx. 30% cell’s energy

4. SODIUM – POTASSIUM PUMP Animation A

5. SODIUM – POTASSIUM PUMP Transmembrane protein 4 subunits 2 large/ 2 small – 3 Na+ binding sites – 2K+ binding sites – ATPase function – 1 site which is phosphorylated 3 Na + moved out, 2 K + moved in Generates electrical potential inside cell (-ve)

6. SODIUM – POTASSIUM PUMP Works by cyclical process flip-flopping between two conformation Flip-flop governed by phosphorylation 3 Na+ bind on cytoplasmic surface Binding changes conformation activating ATPase ATPase phosphorylates the protein, hydrolysing ATP Causes further conformational change Moves 3Na+ to extracellular side Released because phosphorylation also reduces affinity of protein for Na+ (conformational change) 2 K+ bind on extracellular side (conformational change) Dephosphorylation occurs (conformational change) Restores original conformation Protein flips back to cytoplasmic side taking 2K+ with it 2K+ released

7. SODIUM – POTASSIUM PUMP Protein conformation change brought about by covalent modification (phosphorylation) – Changes affinity for Na+/ K+ – Flips the protein’s conformation causing the ions to be moved Dephosphorylation (phosphatase) flips it back Inhibtied by ouabain Bushman’s Poison