Purification and Properties of Na, K-ATPases from the Rectal Gland of Squalus acanthias and the Electric Organ of Electrophorus electricus and Reconstitution of the Na+ - K+Pump from the Purified Enzyme

About twenty years ago Skou (1957) discovered an adenosine triphosphatase in the microsome fraction of the leg nerve of the shore crab which required Mg+, Na+ and K+ for optimal activity. He suggested that this enzyme, which will henceforth be referred to as the Na,K-ATPase, might be involved in the coupled Na+-K+ pump (Baker, 1972), which serves many important physiological functions, such as maintaining osmotic equilibrium in all animal cells, maintaining the gradients of Na+ and K+ in excitable tissues such as nerve and muscle, which permits waves of excitation down their membranes, and effecting transepithelial transport of Na+, and in some cases, K+ in such structures as the intestinal epithelium, the renal tubules, and various glandular structures. It has been estimated that in the mammal about 30% of the ATP which is produced by resting respiration is hydrolyzed via the Na,K-ATPase (Whittam, 1965). Edelman and his coworkers (1974) have demonstrated that thyroid hormone elevates the level of Na,K-ATPase in thyroid-sensitive tissues, and he has suggested that the resultant increased hydrolysis of ATP could be responsible for the calorigenic effect of thyroid hormone.