The Journey of Martin D. Kamen
In the annals of science, few figures embody the turbulent relationship between scientific achievement and political persecution as vividly as Martin David Kamen. A brilliant chemist who co-discovered carbon-14, Kamen enabled a revolution across disciplines from biochemistry to archaeology. His radioactive tracer technique transformed our understanding of life's fundamental processes, yet his career was nearly destroyed by false accusations during the McCarthy era. This is the story of how a nuclear scientist, blacklisted and stripped of his passport, reinvented himself as a pioneering biochemist who unlocked secrets of bacterial cytochromes and photosynthesis, leaving an indelible mark on multiple scientific fields despite decades of adversity.
In the late 1930s, the Radiation Laboratory at the University of California, Berkeley was a hub of cutting-edge nuclear research under the direction of Ernest O. Lawrence, inventor of the cyclotron. Here, a young Martin Kamen, fresh from completing his doctorate in physical chemistry at the University of Chicago, found himself working alongside physicist Samuel Ruben 1 2 . Their mission: to find a radioactive isotope of carbon that could serve as an effective tracer for studying chemical reactions in photosynthesis 1 .
The only radiocarbon known at the time was carbon-11, but with a frustratingly brief half-life of just 21 minutes, it was nearly useless for most biochemical experiments 7 . "By the time you have set up to do a reaction, it has disappeared," as one colleague later explained . Kamen and Ruben needed something longer-lasting.
What followed was a year of tireless experimentation and repeated failures 3 . Then, in January 1940, Kamen began what he would later call a "desperation" experiment 3 . He placed a graphite target inside the laboratory's 37-inch cyclotron, where it absorbed the full beam of deuterons throughout the evening hours for nearly a month 3 .
The breakthrough came on February 27, 1940, when repeated chemical analysis and observation confirmed they had successfully created carbon-14 1 3 . To their astonishment, its half-life was approximately 4,000 years (later refined to 5,730 years), not the short lifespan theorists had predicted 3 . The discovery was nothing short of revolutionary, earning Kamen a place in scientific history—though his collaborator Ruben would never share in the full glory, having died tragically in a laboratory accident just a few years later .
Carbon-14 proved to be what one scientist called "one of the most powerful research tools of this century" 4 . Kamen immediately recognized its potential as a tracer atom in biological systems, developing methodologies that would forever change biochemistry 4 . For the first time, scientists could trace the intricate pathways of carbon through living systems, unraveling the complex networks of reactions that constitute life itself 1 4 .
Carbon-14 allowed researchers to understand all biochemical reactions involving carbon, from photosynthesis to metabolism 4 7 .
In 1949, Willard Libby developed radiocarbon dating, enabling scientists to date artifacts and archaeological finds as far back as 60,000 years 3 .
More recently, carbon-14 has been used to study the distribution and turnover of carbon dioxide in our environment 4 .
The isotope has even helped scholars determine whether pictures were painted by famous artists or by forgers 4 .
As World War II intensified, Kamen and others at the Berkeley Radiation Laboratory were recruited for the Manhattan Project 1 . It was during this period that Kamen first attracted the suspicion of security officials. While working at Oak Ridge, Tennessee, in 1943, he correctly deduced the existence of a nuclear reactor elsewhere in the facility after observing unusual radioactivity in some materials 1 5 . His excitement in reporting this discovery to Ernest Lawrence, overheard by Lawrence's Army escort, triggered an investigation into who had leaked classified information 1 .
The fatal blow came in 1944, when Kamen attended a dinner with two Russian diplomats he had met at a party hosted by his friend, violinist Isaac Stern 1 . The Russians, who were actually undercover KGB officers, sought information about experimental radiation treatments for a colleague with leukemia 1 5 . FBI agents surveilled the dinner and submitted a report alleging Kamen had discussed atomic research 1 .
While the security controversy represented a profound personal and professional crisis, it ultimately led Kamen down an unexpected and fruitful new research path. In 1945, he was hired by Arthur Holly Compton to run the cyclotron program at Washington University in St. Louis 1 . There, and in subsequent positions at Brandeis University and UC San Diego, Kamen's research interests gradually shifted from nuclear physics to biochemistry 2 .
He began studying photosynthetic bacteria instead of green plants, a strategic shift that would yield remarkable discoveries 2 4 . With keen scientific intuition, Kamen recognized that bacteria offered unique advantages for understanding fundamental biological processes 4 .
In 1949, Kamen and his graduate student Howard Gest discovered that the photosynthetic bacterium Rhodospirillum rubrum could produce molecular hydrogen when exposed to light 2 .
In 1953, Kamen and Leo Vernon discovered a c-type cytochrome in Rhodospirillum rubrum, which they named cytochrome c₂ 2 .
These discoveries opened a wholly new area of research—the comparative biochemistry of cytochromes—which would consume much of Kamen's attention for the remainder of his career 2 4 .
As Kamen delved deeper into bacterial cytochromes, he recognized the need to understand their structural foundations. This led to a landmark 1973 study published in the Journal of Biological Chemistry titled "Structural Bases for Function in Cytochromes c. An Interpretation of Comparative X-ray and Biochemical Data" 2 . The research would become one of his most cited contributions to the field.
Kamen and his colleagues employed a comparative approach to understand the relationship between cytochrome c₂ from photosynthetic bacteria and the mitochondrial cytochrome c found in eukaryotes 2 . Though these molecules served analogous functions in their respective electron transport chains, Kamen suspected there might be important structural differences that could reveal insights about their evolution and function.
The study revealed fascinating similarities and differences between the two cytochromes. While both proteins served as electron carriers, Kamen noted that cytochrome c₂ had a more positive electrochemical potential and did not exhibit the large oxidation state-dependent conformational changes characteristic of mitochondrial cytochrome c 2 .
| Property | Cytochrome c₂ | Mitochondrial Cytochrome c |
|---|---|---|
| Electrochemical Potential | More positive | Less positive |
| Conformational Change with Oxidation | Minimal | Significant |
| Physiological Function | Electron transport in bacterial photosynthesis | Electron transport in mitochondrial respiration |
| Structural Flexibility | Less flexible | More flexible |
These structural differences helped explain why cytochrome c₂ couldn't substitute effectively for mitochondrial cytochrome c in eukaryotic systems, despite their similar functions 2 . The findings provided crucial insights into how protein structure evolves to support specific physiological roles in different organisms.
| Cytochrome Type | Source Organism | Key Characteristics |
|---|---|---|
| Cytochrome c₂ | Rhodospirillum rubrum | First characterized bacterial cytochrome; soluble |
| Cytochrome c' | Rhodopseudomonas palustris | Monoheme nature established |
| Cytochrome c₄ | Azotobacter vinelandii | Diheme structure |
| Cytochrome c-551 | Ectothiorhodospira halophila | Isolated from halophilic purple phototrophic bacteria |
The impact of this work extended far beyond understanding a single protein. Kamen's research demonstrated that at least 12 subgroups of cytochromes c existed in nature, each with potential variations in structure and function of the heme group in relation to its protein environment 2 . This revelation opened new perspectives on the molecular diversity of life and how evolution tinkers with successful molecular designs to fit different physiological contexts.
Martin Kamen's extraordinary scientific journey spanned over six decades, leaving an indelible mark on multiple fields. From his discovery of carbon-14 in 1940 to his groundbreaking work on bacterial cytochromes that extended into the 1990s, Kamen exemplified the interdisciplinary spirit that drives scientific progress 1 6 . His career demonstrated how adversity, even in its most painful forms, could be transformed into opportunity.
The honors Kamen received later in life—including the Albert Einstein World Award of Science in 1989 and the Enrico Fermi Award in 1995—provided long-overdue recognition for his contributions 1 7 . Yet his true legacy lies in the countless scientific discoveries made possible by his work. As one colleague noted, "Without carbon-14, biochemistry as we know it today just wouldn't exist" .
His journey from nuclear science to bacterial cytochromes remains an inspiring example of how scientific passion can overcome even the darkest of obstacles, forever changing our understanding of the natural world.
| Years | Position | Key Achievements |
|---|---|---|
| 1936-1944 | Radiation Laboratory, UC Berkeley | Co-discovery of carbon-14; photosynthesis research |
| 1945-1957 | Washington University in St. Louis | Pioneered medical use of radioisotopes; began bacterial photosynthesis studies |
| 1957-1961 | Brandeis University | Helped establish Graduate Department of Biochemistry |
| 1961-1978 | UC San Diego | Founded biochemistry group; continued cytochrome research |
| 1978-2002 | Professor Emeritus | Continued research and writing until his death in 2002 |
Kamen's groundbreaking work across nuclear chemistry and biochemistry relied on several key materials and methodologies. The table below highlights some of the essential "research reagents" that formed the foundation of his experimental approaches.
| Reagent/Material | Function in Research | Scientific Significance |
|---|---|---|
| Graphite Target | Bombarded with deuterons in cyclotron to produce carbon-14 | Enabled creation of the long-lived radioactive carbon isotope 3 |
| Deuterons | Projectiles used in cyclotron bombardment to transform stable isotopes into radioactive ones | Critical for synthesizing various radioisotopes including carbon-14 3 7 |
| Carbon-14 | Radioactive tracer for tracking biochemical pathways | Revolutionized biochemistry by enabling detailed tracking of carbon flow in living systems 1 4 |
| Photosynthetic Bacteria | Model organisms for studying photosynthesis and metabolism | Provided simpler systems than plants for understanding fundamental processes 2 4 |
| Cytochrome c₂ | Bacterial electron transport protein | Model for understanding structure-function relationships in cytochromes 2 6 |
| X-ray Crystallography | Technique for determining atomic structure of proteins | Enabled comparative structural analysis of cytochromes from different species 2 |