Illustration of the Danish biochemist Jens Christian Skou (1918-2018). Skou is best known for his discovery of the first cellular molecular pump, the sodium-potassium pump. The pump, which is found in the membrane of all animal cells, is responsible for maintaining the high concentration of potassium ions and low concentration of sodium ions within a cell by pumping these ions in opposite directions across the plasma membrane, against their concentration gradient. While investigating the breakdown of the energy carrying molecule ATP (adenosine triphosphate), Skou discovered the enzyme sodium-potassium-ATPase in the cell membranes of crab nerve cells. He showed how it was activated and that it promoted the transport of ions through the cell membrane. He was awarded a share of the 1997 Nobel Prize in Chemistry for this discovery.