Hans Krebs: the biochemist who mapped the cell’s energy cycle

In 1937, at the University of Sheffield, Hans Krebs and his colleague William Arthur Johnson established the sequence of reactions now known as the citric acid cycle. The discovery gave scientists a way to understand how cells release energy from food and became one of the foundations of modern biochemistry. It also gave Krebs a lasting place in the history of British science: a German-born physician who, after being dismissed from his post under the Nazi regime, made the decisive work of his career in Britain.

From medical training to a new life in Britain

Hans Adolf Krebs was born in Hildesheim, Germany, on 25 August 1900. His father, Georg, was an ear, nose and throat surgeon; his mother was Alma Krebs, née Davidson. Krebs began studying medicine at Göttingen in 1918, transferred to Freiburg the following year and completed his medical training in Hamburg, earning his MD in 1925. His first scientific paper, published in 1923, concerned a technique for staining tissue. By the time he completed his studies, he had turned from a career as a practising doctor towards medical research, particularly biochemistry.

In 1926 Krebs joined the laboratory of Otto Heinrich Warburg at the Kaiser Wilhelm Institute for Biology in Berlin. He later worked in hospitals in Altona and Freiburg. At Freiburg, he and the medical student Kurt Henseleit investigated how the body forms urea. Their work, published in 1932, established the first metabolic cycle to be discovered, now called the urea cycle or the Krebs–Henseleit cycle. They also developed a solution used to study blood flow in arteries outside the body.

Krebs’s position in Germany ended in 1933. After the Nazi government’s legislation removed people of Jewish ancestry and political opponents from professional posts, he was dismissed from his job at Freiburg. Sir Frederick Gowland Hopkins, a biochemist at the University of Cambridge, intervened on his behalf, and Krebs arrived in Britain in July 1933 with support from the Rockefeller Foundation. He became a naturalised British citizen in 1939.

Research in Sheffield

After a period at Cambridge, Krebs moved to the University of Sheffield in 1935 as a lecturer in pharmacology. The university offered a larger laboratory, and his work there turned to cellular respiration: the processes by which cells make energy available from food. In 1937, Krebs and Johnson established the citric acid cycle, also called the tricarboxylic acid cycle or, after its discoverer, the Krebs cycle.

The discovery was the result of testing possible pathways rather than a sudden leap from an idea to a finished explanation. Krebs used a Warburg manometer to measure oxygen consumption in slices of pigeon breast muscle. He found that compounds including succinate, fumarate and malate increased oxygen consumption. Earlier work by Franz Knoop and Carl Martius had identified reactions involving citrate; Krebs recognised that these findings could help fill gaps in the sequence he was investigating. Over four months of experiments, he and Johnson assembled the cycle.

Krebs first sent a short account to Nature in June 1937, but the journal declined it because its correspondence columns were already full. He then prepared a longer paper, “The Role of Citric Acid in Intermediate Metabolism in Animal Tissues”, which appeared in the Dutch journal Enzymologia. The rejection did not prevent the work from being published, and the pathway it described became central to explanations of cellular metabolism.

Sheffield became the base for a substantial research operation. In 1938, the university opened a Department of Biochemistry, with Krebs as its first head; he became a professor in 1945. He also took charge of the Sorby Research Institute in 1943. The Medical Research Council established its Unit for Cell Metabolism Research at Sheffield in 1944, appointing Krebs as director. He and his team continued to publish research while the department and unit developed.

Beyond the citric acid cycle

The citric acid cycle was not Krebs’s only major contribution to biochemistry. His earlier work on the urea cycle had helped establish how the body forms urea, while later research with Hans Kornberg identified the glyoxylate cycle. In 1957, the two scientists described enzymes that enable a pathway related to the citric acid cycle. The pathway, found in plants, bacteria, protists and fungi, became known as the glyoxylate cycle.

In 1954 Krebs moved with his Medical Research Council unit to the University of Oxford, where he became Whitley Professor of Biochemistry. He held the post until retiring in 1967 and continued his research afterwards, publishing more than 100 papers from the Nuffield Department of Clinical Medicine at the Radcliffe Infirmary. His Oxford career extended the work begun in Sheffield and kept his research group active beyond his formal retirement.

Recognition and remembrance

Krebs shared the 1953 Nobel Prize in Physiology or Medicine with Fritz Lipmann. The award recognised Krebs’s discovery of the citric acid cycle and Lipmann’s work on coenzyme A and acyl-group metabolism. Krebs also received the Albert Lasker Award for Basic Medical Research in 1953, the Royal Society’s Royal Medal in 1954 and its Copley Medal in 1961. He was elected a Fellow of the Royal Society in 1947 and was knighted in 1958.

He married Margaret Cicely Fieldhouse in 1938. They had three children: Paul, Helen and John, who became a biologist and a member of the House of Lords. Krebs died in Oxford on 22 November 1981, aged 81.

His name remains attached to research and teaching in Britain. Oxford’s Department of Biochemistry has honoured him with a plaque marking his years there, and the department hosts the Sir Hans Krebs Prize Lecture Series. Sheffield’s Krebs Institute, founded in 1988, supports interdisciplinary biochemical research. The Biochemical Society has also offered a Krebs Memorial Scholarship for postgraduate study in biochemistry or an allied biomedical science at a British university.

Why Hans Krebs deserves a place in British Legacy

Krebs’s British legacy rests on work carried out in British universities and research institutions, not simply on the later adoption of his name for a scientific pathway. After losing his post in Germany in 1933 because of his Jewish ancestry, he found a place at Cambridge and built his most celebrated research programme at Sheffield. There, the cycle established with William Arthur Johnson gave biochemists a framework for understanding a central part of cellular respiration. Its influence extends beyond one university or one award: it remains part of the basic account of how living cells make energy available.

His contribution was also broader than the discovery that became best known. The urea cycle, the glyoxylate cycle and the research groups he led at Sheffield and Oxford show a sustained effort to describe how biological processes work, step by step. His Nobel Prize and scientific honours marked recognition of that achievement, while the research institute, lecture series and scholarship named for him keep his connection to British science active in teaching and research. Krebs’s story also carries a particular historical significance: Britain’s universities gave a scientist expelled by Nazi policy the opportunity to continue his work, and that work became part of the country’s scientific inheritance.

Sources

Hans Krebs (biochemist), revision 1372003043 · Hans Krebs (biochemist)

Adapted in part from Hans Krebs (biochemist) by Wikipedia contributors, under CC BY-SA 4.0. Text has been edited and combined with the existing article; this adapted text is shared under the same licence. Contributor history.