David Keilin (1887–1963): The Architect of Cellular Respiration
David Keilin was a polymathic biologist whose work bridged the gap between the microscopic structure of organisms and the chemical reactions that sustain life. Though he began his career as an entomologist and parasitologist, he is most revered today as a founding father of modern biochemistry. His "rediscovery" of cytochrome transformed our understanding of how cells breathe, providing the missing link in the machinery of energy production.
1. Biography: From Warsaw to Cambridge
David Keilin was born on March 21, 1887, in Moscow to Polish parents. His family returned to Warsaw during his childhood, where his early education was hampered by chronic asthma—a condition that would influence his quiet, laboratory-focused lifestyle for years to come.
Keilin’s academic journey was international and prestigious:
- Education: He studied at the University of Liège in Belgium and the Sorbonne in Paris. In Paris, he worked under the renowned biologist Maurice Caullery, focusing on the life cycles of parasitic insects.
- Move to Cambridge: In 1915, Keilin moved to the University of Cambridge to serve as a research assistant to George Nuttall, the first Quick Professor of Biology.
- Career Trajectory: Keilin spent the remainder of his life at Cambridge. In 1931, he succeeded Nuttall as the Quick Professor of Biology and became the Director of the Molteno Institute for Parasitology. Under his leadership, the Molteno Institute became a world-renowned center for cellular and enzyme research.
Keilin remained active in research until the very end of his life, passing away on February 27, 1963, during a faculty meeting at Cambridge.
2. Major Contributions: The Respiratory Chain
Keilin’s most profound contribution was the discovery (or more accurately, the definitive characterization) of cytochrome.
The Rediscovery of Cytochrome (1925)
While studying the horse-bot fly (Gasterophilus), Keilin noticed a pigment that changed color when the insect's muscles contracted. Using a microspectroscope, he observed four distinct absorption bands that appeared and disappeared based on oxygen availability. He realized this was a respiratory pigment present in almost all living cells—from yeast to humans. He named it "cytochrome" (cellular pigment).
The Respiratory Chain
Keilin demonstrated that cytochromes act as an intermediary in cell respiration, transferring electrons from food molecules to oxygen. This effectively mapped out the "respiratory chain," the fundamental process by which cells generate energy (ATP).
Enzymology
Beyond cytochromes, Keilin made landmark discoveries regarding enzymes. Along with his colleague T. Mann, he discovered and isolated carbonic anhydrase, the enzyme responsible for the rapid interconversion of carbon dioxide and water in the blood. He also performed pioneering work on catalase, peroxidase, and polyphenol oxidase.
Anabiosis and Cryptobiosis
Keilin was fascinated by how organisms survive extreme dehydration or freezing. He coined the term cryptobiosis to describe a state of "hidden life" where metabolic activity comes to a reversible standstill, a concept crucial to modern cryobiology.
3. Notable Publications
Keilin was a meticulous writer who preferred quality over quantity. His most influential works include:
- "On cytochrome, a respiratory pigment, common to animals, yeast, and higher plants" (1925): Published in the Proceedings of the Royal Society, this is considered one of the most important papers in the history of biochemistry.
- "Cytochrome and intracellular oxidase" (1929): This paper further elucidated the relationship between the pigment and the enzymes that drive oxidation.
- "Carbonic anhydrase: Purification and nature of the enzyme" (1940): Co-authored with T. Mann, this established the role of zinc in enzyme function.
- "The History of Cell Respiration and Cytochrome" (1966): Published posthumously and edited by his daughter, Joan Keilin, this book is both a scientific treatise and a definitive historical account of the field.
4. Awards & Recognition
Keilin’s work earned him the highest honors in the scientific community, though he famously never received the Nobel Prize—an omission many historians consider one of the committee’s significant oversights.
- Fellow of the Royal Society (1928)
- Royal Medal (1939): Awarded by the Royal Society for his contributions to biochemistry and entomology.
- Copley Medal (1951): The Royal Society’s highest award, recognizing his "fundamental researches in the fields of protozoology, entomology and the biochemistry of enzymes."
- Leeuwenhoek Medal (1958): Awarded by the Royal Netherlands Academy of Arts and Sciences for his work in microbiology.
- Honorary Degrees: He received honorary doctorates from universities including Utrecht, Bordeaux, and Liège.
5. Impact & Legacy
David Keilin is often described as the man who turned "biological chemistry" into "biochemistry."
- Bioenergetics: His work on the respiratory chain provided the framework for Peter Mitchell’s later "chemiosmotic theory" (which won the Nobel Prize in 1978). Without Keilin’s mapping of the electron transport system, our understanding of mitochondria would be non-existent.
- The Molteno Institute: He transformed a small parasitology lab into a powerhouse of biochemical research, training a generation of scientists who would go on to lead the "molecular revolution."
- The Comparative Method: Keilin’s unique strength was his ability to see the unity in biology. He applied the same rigor to studying a parasitic worm as he did to a complex human enzyme, proving that the chemical basis of life is universal.
6. Collaborations
Keilin was a collaborative scientist who fostered a close-knit intellectual environment at the Molteno Institute.
- T. Mann: His primary collaborator on enzyme research, particularly the discovery of carbonic anhydrase and studies on hemoproteins.
- E.F. Hartree: Worked closely with Keilin for decades on the purification and spectral analysis of cytochromes.
- George Nuttall: His early mentor who provided the institutional support Keilin needed to establish himself in England.
- Joan Keilin: His daughter, a biochemist in her own right, who collaborated with him in his later years and ensured his final research was published after his death.
7. Lesser-Known Facts
- The "Lost" Predecessor: Keilin was not actually the first to see cytochrome. In the 1880s, an Irish physician named C.A. MacMunn discovered a pigment he called "myohematin." However, MacMunn’s work was harshly (and incorrectly) criticized by the influential Felix Hoppe-Seyler, and it was forgotten. Keilin discovered it independently but spent significant effort in his 1925 paper and his 1966 book giving MacMunn the credit he had been denied.
- The Handheld Spectroscope: Keilin’s primary tool was a simple, vintage Zeiss microspectroscope. While other scientists were moving toward massive, expensive machinery, Keilin used this handheld device to make some of the 20th century’s greatest biological discoveries.
- The War Effort: During WWII, despite the dangers of the Blitz, Keilin refused to leave the Molteno Institute. He spent many nights on the roof of the building acting as a fire-watcher to protect the laboratory and its vital research.
- The Reluctant Lecturer: Despite his brilliance, Keilin was known for a quiet, almost whispering voice due to his asthma. Nevertheless, his lectures were legendary for their clarity and the infectious enthusiasm he held for the "beauty" of biochemical reactions.