Hans Krebs (biochemist)
Citric acid cycle (Krebs cycle)

At the University of Sheffield, Krebs and William Arthur Johnson investigated cellular respiration by which oxygen was consumed to produce energy from the breakdown of glucose. Krebs had earlier suggested to Warburg while they worked together in Germany that by using a manometer it could be possible to detect the oxygen consumption and identify the chemical reaction in glucose metabolism. Warburg had flatly rejected the idea. In Sheffield, Krebs vigorously worked to identify a possible chemical reaction and came up with numerous hypothetical pathways. Using the manometer he tested those hypotheses one by one. One hypothesis involving succinate, fumarate, and malate proved to be useful because all these molecules increased oxygen consumption in the pigeon breast muscle. In 1937, German biochemists Franz Knoop and Carl Martinus had demonstrated a series of reactions using citrate that produced oxaloacetate. Krebs realised that these molecules could be the missing intermediates for such reaction. After four months of experimental works to fill in the gaps, Krebs and Johnson succeeded in establishing the sequence of the chemical cycle, which they called the " citric acid cycle ". It is also known as the "Krebs cycle" or " tricarboxylic acid (TCA) cycle".

Krebs sent a short manuscript account of the discovery to Nature on 10 June 1937. On 14 June, he received a rejection letter from the editor, saying that the journal had "already sufficient letters to fill correspondence columns for seven or eight weeks", and encouraging Krebs to "submit it for early publication to another periodical."

Krebs immediately prepared a longer version titled "The Role of Citric Acid in Intermediate Metabolism in Animal Tissues", which he sent to the Dutch journal Enzymologia after two weeks and was published in two months. It was followed by a series of papers in different journals.
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