Dr. Christian de Duve, a Belgian biochemist whose discoveries about the internal workings of cells shed light on genetic disorders like Tay-Sachs disease and earned him a Nobel Prize in 1974, died at his home in Nethen, Belgium, on Saturday. He was 95.
The cause was euthanasia, which is legal in Belgium, and which was administered by two doctors at Dr. de Duve's request, his son Thierry said.
"He was suffering from a number of health problems," including cancer and arrhythmia, Dr. Günter Blobel, a colleague of Dr. de Duve's at the Rockefeller University in Manhattan, said, and decided to end his life after falling a few weeks ago. "He wanted to make the decision while he was still able to do it and not be a burden."
Dr. de Duve spent the last month writing letters to friends and colleagues telling them of his decision, and he put off his death until his son Thierry, who lives in Los Angeles, and his three other children could be with him, Dr. de Duve told the Belgian newspaper Le Soir in an interview published after his death.
Beginning in the late 1940s, Dr. de Duve used a centrifuge and other techniques to separate and examine the inner components of cells. He discovered the lysosome, a tiny sack filled with enzymes that functions like a garbage disposal, destroying bacteria or parts of the cell that are old or worn out.
His discoveries helped unravel the biology of Tay-Sachs disease and more than two dozen other genetic diseases in which a shortage of lysosomal enzymes causes waste to accumulate in cells, eventually destroying them. In Tay-Sachs, a buildup of fatty substances in the brain and other tissues leads to blindness, paralysis, mental retardation and death.
After learning he had been awarded a Nobel, Dr. de Duve said that although his discoveries brought great intellectual satisfaction, his goal was to use them to conquer disease. "It's now time to give mankind some practical benefit," he said.
Dr. de Duve shared the 1974 Nobel Prize in Physiology or Medicine with Dr. Albert Claude, who first used centrifugal techniques to glance inside cells, and Dr. George E. Palade, who pioneered using the electron microscope to better understand cell structures. Dr. Claude died in 1983; Dr. Palade died in 2008.
Before the scientists embarked on their research, the cell was perceived as a work basket containing indeterminate parts. The scientists, working separately, transformed that view with discoveries of important cell components.
Dr. Claude discovered mitochondria, which store energy, and Dr. Palade discovered ribosomes, the protein factories within cells. The Karolinska Institute, in awarding the Nobel, credited the three scientists with giving birth to the field of modern cell biology.
Christian René de Duve was born on Oct. 2, 1917, in Thames Ditton, England, near London. His parents were Belgians who had fled to England during World War I. When the war ended, his family returned to Belgium and settled in Antwerp, where Dr. de Duve grew up. He received his medical degree from the Catholic University of Louvain in 1941.
Dr. de Duve served as a medic in the Belgian Army during World War II. His unit was sent to France, where German forces captured it. But Dr. de Duve escaped and made his way back to Belgium.
He resumed his medical training, accepting an internship at the Catholic University of Louvain's Cancer Institute while pursuing graduate studies in chemistry. He wrote a book on insulin, the subject of his thesis. He received his doctorate in chemistry in 1945.
Intent on a career in research, he set off for labs in Sweden and the United States to study biochemistry. Over the next two years, he studied under Hugo Theorell at the Medical Nobel Institute in Stockholm and Carl Cori and Gerty Cori at Washington University in St. Louis, all of whom would later receive Nobel Prizes. Dr. de Duve returned to the Catholic University of Louvain in 1947 to teach physiological chemistry, and became a full professor in 1951.
His research continued to focus on insulin, a hormone involved in the regulation of blood sugar. Working with liver cells, he used Dr. Claude's recently developed centrifugal techniques to separate cell parts. Centrifuges are spinning devices that speed the rate at which particles settle in liquid. Dr. Claude's technique called for using a pestle to break open cells before placing them in the centrifuge.
In one experiment, Dr. de Duve noticed that acid phosphatase, an enzyme he had included as a control, was less active than in earlier experiments in which he had used an electric blender instead of a pestle to break up cells. Dr. de Duve was intrigued and pursued his chance finding.
"My curiosity got the better of me," he wrote in his Nobel autobiography, "and as a result, I never elucidated the mechanism of action of insulin."
In further experiments, Dr. de Duve found that the enzyme was contained in some sort of membrane; cells broken up in the blender released more of the enzyme because the membrane suffered greater damage. Because the enzyme was so acidic, he concluded its only purpose could be digestion. He called the membrane lysosome, and later identified it in pictures taken with an electron microscope.
After Dr. de Duve's discovery, other researchers went on to identify more than 50 lysosomal enzymes and some genetic diseases that result when an enzyme either is absent or does not function properly. Today some of these conditions, like Pompe disease, which causes sugar to accumulate in the liver and other organs, are treated with drugs that supply the needed enzyme. Other illnesses, like Tay-Sachs disease, have no effective treatments.
"We are sick because our cells are sick," Dr. de Duve said.
Dr. de Duve became a professor at the Rockefeller University in 1962 and began splitting his time between his laboratories there and at Louvain. In 1974, he founded the International Institute of Cellular and Molecular Pathology in Brussels.
He became emeritus professor at the Catholic University of Louvain in 1985 and at Rockefeller in 1988. He retired as president of the pathology institute in 1991.
In his later years, he applied his knowledge of biochemistry to the study of the origins of life. He wrote several books, including "A Guided Tour of the Living Cell" (1984), "Blueprint for a Cell" (1991), "Vital Dust" (1995) and "Genetics of Original Sin: The Impact of Natural Selection on the Future of Humanity" (2012).
Besides his son Thierry, survivors include another son, Alain; two daughters, Anne and Françoise; two brothers, Pierre and Daniel; seven grandchildren; and two great-grandsons.
In his interview with Le Soir, Dr. de Duve said he was at peace with his decision to end his life. "It would be an exaggeration to say I'm not afraid of death," he said, "but I'm not afraid of what comes after, because I'm not a believer."
Daniel E. Slotnik contributed reporting.nation
This article originally appeared in The New York Times.