What is Na+-K+ ATPase is which type of pump- and explain in detail?
Ans. is 'b' i.e., Electrogenic Na+ -K+ ATPase (Na+K+ 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.