<prompt> Na-K ATPase is which type of pump-Secondary activeElectrogenicSymportAll of the above  <response>: Ans. is b i.e., Electrogenic Na -K ATPase NaK pump Sodium-potassium pump is the most important pump for primary active transport in the body. Na-K pump is an electrogenic pump that is responsible for maintaining the Na and K concentration difference across the cell membrane. Na - K pump extrudes 3 Na out from the cell and at the same time pump 2K into the cell, i.e., Coupling ratio of Na K pump is 3 : 2. Na and K transport by Na - K pump is primary active transport and both Na and K are transported against concentration gradient intracellular fluid has high concentration of K and ECF has high concentration of Na. Na K pump uses energy by hydrolysing ATP; this pump contain ATPase activity.Structure Na - K pump is a carrier protein which is a heterodimer made up of two separate globular proteins: a larger one called a-subunit with molecular weight of 100,000 and a smaller one called b-subunit, with a molecular weight of about 55,000. Both a- and b- subunits span across the membrane with an intracellular and an extracellular sites. Na and K transport occurs through a-subunits. Intracellular portion of a-subunit has three Na binding sites three receptor sites for Na, an ATP binding site, a phosphorylating site and ATPase activity. Extracellular portion has two K binding sites two receptor sites for K, and an oubain binding site. The b-subunit has three extracellular glycosylation sites, all of which appear to have attached carbohydrate residue.Function The Na - K pump is an electrogenic pump since it produces a net movement of positive charge out of the cell. Thus, besides maintaining the ionic composition of the intracellular fluid, the Na - K pump helps to maintain the electrochemical potential difference across the cell membrane. However, Na - K pump contributes only 4 millivolts to total resting membrane potential of 90 volts which is almost negligble. Active transport of Na and K is one of the major energy using process in the body. On the average, it accounts for about 24 of the energy utilized by cell and in neurons it accounts for 70. Activity of Na - K pump is stimulated by increased intracellular concentration of Na, thyroid hormones, aldosterone and insulin. Pump activity is inhibited by CHF, CRF, digoxin toxicity and dopamine. 