Krebs, Hans Adolf (1900–1981)

The purpose of the Krebs (or tricarboxylic acid) cycle is to complete the biochemical breakdown of food to produce energy-rich molecules, which the organism can use to fuel work. Acetyl coenzyme A (acetyl CoA) – produced by the breakdown of sugars, fatty acids, and some amino acids – reacts with oxaloacetic acid to produce citric acid, which is then converted in a series of enzyme-catalysed steps back to oxaloacetic acid. In the process, molecules of carbon dioxide and water are given off, and the precursors of the energy-rich molecules ATP are formed. (The numbers in the diagram indicate the number of carbon atoms in the principal compounds.)

German-born British biochemist who was awarded a Nobel Prize for Physiology or Medicine in 1953 for his discovery of the citric acid cycle, also known as the Krebs cycle, the final pathway by which food molecules are converted into energy in living tissues. He was knighted in 1958.

Krebs first became interested in the process by which the body degrades amino acids. He discovered that nitrogen atoms are the first to be removed (deamination) and are then excreted as urea in the urine. He then investigated the processes involved in the production of urea from the removed nitrogen atoms, and by 1932 he had worked out the basic steps in the urea cycle.

Krebs was born in Hildesheim and studied at the universities of Göttingen, Freiburg, Munich, Berlin, and Hamburg. In 1933, with the rise to power of the Nazis, he moved to the UK, initially to Cambridge and to Sheffield in 1935. He was professor at Sheffield 1945–54, and at Oxford 1954–67.