Membrane Adenosine Triphosphatase as a Participant in the Active Transport of Sodium and Potassium in the Human Erythrocyte

Abstract

Robert Lickely Post was born in 1920 in Philadelphia. He was educated at Harvard University, receiving his B.S. in 1942 and his M.D. in 1945. He spent a year as an intern at Hartford Hospital in Connecticut before becoming an instructor at the University of Pennsylvania Medical School. In 1948, Post moved to Nashville, where he joined the faculty at Vanderbilt University. He progressed from instructor to professor at the medical school and remained there until 1991. He is currently a visiting scholar at the University of Pennsylvania Medical School. Post is best known for his work on the sodium and potassium ion transport adenosine triphosphatase (Na,K-ATPase). The enzyme is embedded in the plasma membrane of animal cells and transports Na and K across the membrane. Transport is stoichiometrically coupled to the hydrolysis of cytoplasmic ATP. Three Na ions are transported outward, and two K ions are transported inward for every one terminal phosphate group of ATP hydrolyzed. Post started working on the kinetics of active sodium and potassium transport in human erythrocytes in 1954 while at Vanderbilt. Then, in 1957, Jens C. Skou published a paper on ATPase activity in crab nerves (1) in which he reported that the ATPase activity required both sodium and potassium ions simultaneously. Skou concluded, “Characteristics of the system suggest that the ATPase studied here may be involved in the active extrusion of sodium for the nerve fiber.” Post decided to search for the same activity in ATPase from human erythrocytes. His studies are the subject of the Journal of Biological Chemistry (JBC) Classic reprinted here. In the Classic, Post, along with his students Cullen Merrit, Richard Kinsolving, and Charlie Albright, report on their identification of an insoluble ATP-cleaving enzyme system involved in the active transport of sodium outward and potassium inward across the membranes of human erythrocyte membranes. They observed that both activities were located in the membranes and that both required sodium and potassium ions together. This paper not only provided a method for identifying a transport system in a preparation of broken membranes but also showed that ions, which were considered simple cofactors, could also be substrates for translocation. The Classic was recognized as a Current