Two American scientists share this year's Nobel Prize in Chemistry for clarifying how water and ions are transferred into and out of cells. The committee commended the work of Peter Agre of the Johns Hopkins University and Roderick MacKinnon of the Howard Hughes Medical Institute at Rockefeller University for unveiling "a fantastic family of molecular machines: channels, gates and valves, all of which are needed for the cell to function." The researchers will each receive half of the 10 million Swedish kronor (about $1.3 million) prize.

Even though the human body is nearly 70 percent water, it was not always clear just how water is transported between cells. Agre (above, left) determined that a protein isolated from cell membranes in the late 1980s is the key to this process. Discovery of this long-sought water channel allowed scientists to follow in detail a water molecule on its way through cell membranes. In addition, the finding elucidated why only water--and not other small molecules or ions--can pass through the channel. Dubbed aquaporin, the proteins are vital to proper functioning of a variety of organs including the kidneys, which process urine and allow most of the water to be reabsorbed by the body.

MacKinnon (above, right) was honored for his work with a different type of membrane channel: the ion channel. These passageways permit selected ions, notably potassium and sodium, to pass from cell to cell. Such signaling allows muscles and the nervous system to function correctly. In 1998, MacKinnon determined the structure of the potassium ion channel using x-ray crystallography and illustrated why potassium ions can navigate it whereas smaller sodium ions cannot. Because disturbances in ion channels can lead to a variety of ailments, including cystic fibrosis and cardiac arrhythimia, the finding should help scientist develop novel pharmaceutical treatments.