Jens Christian Skou, a Danish physiologist who won the Nobel Prize in chemistry for discovering a molecular pump crucial to living cells and organisms, died May 28. He was 99.

Aarhus University in Denmark, where Dr. Skou had been an emeritus professor since 1988, announced the death in a statement but did not give a cause.

Operating almost imperceptibly, on an infinitesimally tiny scale, the pump that Dr. Skou discovered makes possible a rebalancing of the quantities of charged ions that face each other across a cell membrane.

Differences in their concentration create an electrical potential or voltage, which in turn makes it possible for the nerve cells Dr. Skou studied to signal each other — and other organs of the body — through the exchange of minute electrical currents.

Dr. Skou received the Nobel in 1997, sharing the prize with the team of Paul D. Boyer and John E. Walker, who showed how all living things make adenosine triphosphate (ATP), a molecule that stores energy. Dr. Skou discovered the enzyme known as sodium-potassium-stimulated adenosine triphosphatase, which maintains the balance of sodium and potassium ions in the cell.

Its mechanism was not obvious. Dr. Skou recalled that critics scoffed at his claims that an enzyme could move ions across the membranes enveloping cells.

His work was fueled by a background in medicine and surgery, in which anesthetics are used to block the transmission of signals produced by sensation. Nerve cells transmit sensation through a molecular process akin to charging a battery, using the battery to generate a current and then recharging the battery.

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The sodium-potassium pump is an important key to the charging and recharging, and blocking its action can make the body numb to sensation.

It seemed that mere curiosity was the motivation for the experiments that ultimately led to Dr. Skou’s major discovery. For much of his career he was known for emphasizing the importance of such research, which he pursued to answer fundamental questions as much as to bring immediate applications. His discovery pointed the way to new treatments for disease and for correcting physiological defects.

Dr. Skou was born in Lemvig, Denmark, on Oct. 8, 1918. His father and uncle were in the timber and coal business.

As he told it, the decision to pursue medicine came from a combination of factors, including a suggestion from his tennis partner and the need for some recognizable goal.

He obtained a medical degree from the University of Copenhagen in 1944, training for seven years amid the German occupation of Denmark.

At one point, he wrote in a biographical sketch for the Nobel, he learned that “one of our medical classmates was a German informer. We knew who he was, so we could take care.” After the suspected informer “was eventually liquidated,” Dr. Skou said, the students feared reprisal and stayed away from classes. After exams were taken and passed, the Hippocratic oath was administered in secret.

Dr. Skou developed his interest in surgery as an intern, in part because his supervisor showed a great interest in bringing him along quickly.

He soon discovered the reason. One night the two began treating a patient with appendicitis. In the middle of the operation, Dr. Skou was told to take over, and his supervisor left. After completing the procedure, Dr. Skou learned that his supervisor had gone to pick up weapons that had been dropped by parachute to the Danish resistance.

Dr. Skou went on with surgery. But in the surgical ward, curiosity over the effects of local anesthetics became a major source of motivation, and in 1947, he joined the Institute for Medical Physiology at Aarhus University. He was almost 30, and aside from the science requirements of his medical education, he said he “had no scientific training.”

His research in local anesthetics eventually enabled him to identify the sodium-potassium pump, which he first described in a 1957 paper.

Dr. Skou served two stints as head of the physiology department at Aarhus, beginning in 1963 and again in 1978.

Survivors include his wife, Ellen Margrethe Nielsen, and two daughters. The couple’s first daughter was born in 1950 with a fatal disease and died before she was 2.