Hans Adolf Krebs

1900-1981

German-born British Biochemist

Hans Adolf Krebs won the 1953 Nobel Prize for physiology or medicine, which he shared with American biochemist Fritz Albert Lipmann (1899-1986), for his studies of intermediary metabolism, especially his discovery of the metabolic pathway known as the tricarboxylic acid (TCA) cycle, or Krebs cycle, the major source of energy in living organisms. In the presence of oxygen, the reactions of the TCA cycle result in the conversion of the metabolic products of sugars, fats, and proteins into carbon dioxide, water, and energy-rich compounds. Krebs was also involved in the discovery of the metabolic pathway known as the urea cycle. The urea cycle allows ammonia to be converted into urea, a less toxic substance that is excreted in the urine of most mammals. This cycle also serves as a source for the amino acid arginine.

Krebs was born in Hildesheim in Hanover, Germany. His father, Georg Krebs, was an ear, nose, and throat surgeon. After completing his studies at the Hildesheim Gymnasium, Krebs decided to study medicine and join his father's successful practice. He was drafted into the army in 1918, but was discharged shortly afterward when World War I ended. From 1918 to 1923 he studied medicine at the universities of Göttingen, Freiburg-im-Breisgau, and Berlin. During this period, he became interested in the new field of intermediary metabolism. Krebs obtained his M.D. from the University of Hamburg in 1925 and spent one year of required medical service at the Third Medical Clinic of the University of Berlin. After taking a special chemistry course for medical students in Berlin, he became assistant to Otto Warburg (1883-1970) at the Kaiser Wilhelm Institute for Biology at Berlin-Dahlem. Here, Krebs learned techniques, involving manometry and tissue slices, that Warburg had developed to study glycolysis and cellular respiration. Krebs remained at the Institute until he returned to hospital work in 1930. During the next three years, he combined research on the biosynthesis of urea with clinical work at the Municipal Hospital at Altona and the Medical Clinic of the University of Freiburg-im-Breisgau.

In June 1933 the National Socialist government terminated his appointment and he left Nazi Germany for England. He was invited by Sir Frederick Gowland Hopkins (1861-1947) to join the School of Biochemistry at the University of Cambridge. Krebs held a Rockefeller Studentship until 1934, when he became a demonstrator of biochemistry at Cambridge. In 1935 he was appointed a lecturer in pharmacology at the University of Sheffield; three years later, he was put in charge of the department of biochemistry and married Margaret Cicely Fieldhouse, a teacher of domestic science, with whom he had three children. In 1945 Krebs was promoted to professor and became director of a Medical Research Council unit established in his department. In 1954 he was appointed Whitley Professor of Biochemistry at the University of Oxford, and the Medical Research Council's Unit for Research in Cell Metabolism was transferred there. During World War II, Krebs carried out research on special diets that might be useful as supplements in times of scarcity. From 1954 to 1967 Krebs served on the faculty at Oxford.

During his long and distinguished research career, Krebs investigated many problems related to intermediary metabolism, including the synthesis of urea in the mammalian liver, the synthesis of uric acid and purine bases in birds, the intermediary stages of the oxidation of foodstuffs, the mechanism of the active transport of electrolytes, and the relationship between cell respiration and the generation of adenosine polyphosphates. One of the great landmarks in biochemistry was his demonstration of the existence of a cycle of chemical reactions involved in the breakdown of sugars and resulting in the formation of citric acid; the TCA cycle liberates carbon dioxide and electrons, which are used in the creation of high-energy phosphate bonds in the form of adenosine triphosphate (ATP), the chemical-energy reservoir of the cell.

Krebs earned many other awards and honors in addition to the Nobel Prize. He was elected a fellow of the Royal Society of London in 1947 and knighted in 1958. He was awarded the Copley Medal; the Gold Medal of the Netherlands Society for Physics, Medical Science, and Surgery; and honorary degrees from many universities.

LOIS N. MAGNER