| English biochemist Date of Birth: 25.08.1900 Country: Great Britain |
Hans Adolf Krebs was born in Hildesheim, Germany, into a family of otorhinolaryngologist Georg Krebs and Alma Krebs (Davidson). He received his primary education at Andreanum Gymnasium in Hildesheim and graduated in 1918. During the last months of World War I, Krebs served in the Prussian Army's communication regiment. He then studied medicine at the Universities of Göttingen, Freiburg, Munich, and Berlin, receiving his medical degree from the University of Hamburg in 1925. Krebs spent a year studying chemistry at the Institute of Pathology at the University of Berlin and then began working as a laboratory assistant to Otto Warburg at the Kaiser Wilhelm Institute for Biology in Berlin. Warburg developed an experimental method for studying cellular respiration – the consumption of oxygen and the production of carbon dioxide during the metabolism of carbohydrates, fats, and proteins. Instead of studying respiration in intact animals or investigating whole organs, Warburg used thin slices of fresh tissue placed in an airtight vessel with a pressure gauge. When the tissue absorbed oxygen during biochemical reactions, the pressure in the vessel decreased, providing an objective measure of respiratory activity. In 1930, Krebs returned to clinical medicine and started working as an assistant in a municipal hospital in Altona, Hamburg, and as a lecturer at the University of Freiburg Medical Clinic. During this time, he continued his biochemical research. Using a similar experimental setup to Warburg's, he described the urea cycle, a process by which the end products of nitrogen metabolism are removed from the body. He discovered that the amino acid ornithine, when added to liver slices, acted as a catalyst for this cycle, accelerating urea synthesis without being consumed itself. It was found that ornithine is converted into a similar amino acid called citrulline, which in turn is converted into the amino acid arginine. Arginine is then broken down into urea and ornithine, and the entire cycle repeats itself. Krebs' development of the concept of cyclic processes in biochemistry brought him worldwide recognition.
When Adolf Hitler came to power in Germany in 1933, Krebs, who was Jewish, lost his job at the University of Freiburg. However, the Rockefeller Foundation provided him with the opportunity to study biochemistry under the guidance of Frederick Gowland Hopkins at the University of Cambridge's Biochemical Laboratory in the United Kingdom. In 1933, Krebs arrived in Cambridge, taking with him "practically nothing but a sigh of relief, a few books, and 16 packages of Warburg vessels." He started working as a Demonstrator in Biochemistry and soon obtained his Master's degree. In 1935, he was appointed a lecturer in Pharmacology at the University of Sheffield. The following year, Zionist leader Chaim Weizmann invited Krebs to work at the Jewish University's Institute of Biochemistry, which was being established in Rehovot, Palestine. However, the limited research opportunities at the Jewish University, coupled with the outbreak of the Arab-Israeli conflict, led Krebs to decide to stay in England, where he was appointed a part-time lecturer in Biochemistry at the University of Sheffield. In 1937, while studying the intermediary stages of carbohydrate metabolism, Krebs made another significant discovery in biochemistry. He described the citric acid cycle, or the tricarboxylic acid cycle, which is now commonly known as the Krebs cycle. This cycle represents the common final pathway of the breakdown of carbohydrates, proteins, and fats into carbon dioxide and water and serves as the main source of energy for most living organisms. Earlier works by Albert Szent-Györgyi, Franz Knoop, Carl Martius, and other researchers had shown that in the presence of oxygen, citric acid (a six-carbon tricarboxylic acid) is converted into oxaloacetic acid (a four-carbon tricarboxylic acid) and carbon dioxide through a series of reactions.
The concept of the Krebs cycle allows us to understand how energy is generated from nutrients in the body. Krebs studied the sequence of energy conversion from nutrients to other compounds in the body. By analyzing the formulas of more than 20 organic acids closely related to carbohydrates, Krebs found that lactic acid and pyruvic acid can go through a specific sequence of transformations. Ultimately, he focused on pyruvic acid in his experiments. Through experimental evidence, Krebs demonstrated that during the oxidation of pyruvic acid, an intermediate compound called acetyl-CoA (Coenzyme A) is formed. Additionally, he discovered that this oxidation process releases carbon dioxide and produces other acids, with the entire process repeating itself upon the involvement of the next molecule of Coenzyme A. Krebs established that the fundamental principles of his cycle also applied to other nutrients, particularly fatty acids.
The discovery of the cyclic nature of intermediary metabolic reactions was a milestone in the development of biochemistry, as it provided a key to understanding metabolic pathways. It also stimulated further experimental work and broadened the understanding of cellular reaction sequences. In 1939, Krebs obtained British citizenship. During World War II, he led research at the Medical Research Council on nutrition, including studies on the requirements for vitamins A and C. In 1945, Krebs was appointed a professor and head of the Department of Biochemistry and Director of the Medical Research Council's Cell Metabolism Unit at the University of Sheffield.
In 1953, Krebs was awarded the Nobel Prize in Physiology or Medicine "for the discovery of the citric acid cycle." He shared the prize with Fritz Lipmann. In his congratulatory speech, researcher Eric Hammarskjöld from the Karolinska Institute stated, "The Krebs cycle explains two simultaneously occurring processes: energy-releasing reactions and synthetic reactions that utilize this energy." In Krebs' Nobel lecture, he summarized his discoveries in the field of the citric acid cycle. Concluding his "excursion into general biology," he analyzed the broader significance of these findings. "The presence of the same energy-generating mechanism in all living creatures allows us to draw two conclusions," he said. "First, this mechanism originated at very early stages of evolution, and second, life as we know it originated only once." A year after receiving the Nobel Prize, Krebs was appointed as the Professor of Biochemistry at the Nuffield Department of Clinical Medicine at the University of Oxford, where the Medical Research Council's Cell Metabolism Unit was relocated. Three years later, Krebs and his former student, Hans Kornberg, discovered a variant of the citric acid cycle known as the glyoxylate cycle, in which two molecules of Coenzyme A are converted into succinic acid. This cycle has more significance for metabolic processes in plant and microbial cells than in animal cells. Krebs and Kornberg collaborated on the book "Energy Transformation in Living Matter: A Survey" (1957), which discussed the citric acid cycle and its function in living organisms.
After retiring from the University of Oxford in 1967, Krebs was appointed as a Consulting Professor of Biochemistry at the Royal Free Hospital Medical School in London. He continued his research on the regulation of metabolic reactions, "inborn errors of metabolism," and liver preservation for transplantation at the Nuffield Department of Clinical Medicine at the University of Oxford. Krebs was critical of "expensive and unproductive" university research and government policies.
He once compared his attempts to explain the chemical processes occurring in living cells to searching for missing pieces of a mosaic puzzle. In 1938, Krebs married Margaret Cicely Fieldhouse. They had two sons and a daughter. On November 22, 1981, Krebs passed away in Oxford at the age of 81.
Krebs received numerous awards, including the Lasker Award from the American Public Health Association (1953), the Royal Medal (1954) and Copley Medal (1961) from the Royal Society, and the Gold Medal from the Royal Medical Society (1965). In 1958, Krebs was knighted by Queen Elizabeth II. He was a foreign member of the National Academy of Sciences and the American Academy of Arts and Sciences. He also served as a Fellow of the American College of Physicians and a member of the Weizmann Institute of Science in Israel.