[9] Near the end of World War I, in September 1918, six months short of completing his secondary school education, he was conscripted into the Imperial German Army.

[10] Krebs decided to follow his father's profession and entered the University of Göttingen in December 1918 to study medicine.

[10][14][15] In 1926, Krebs joined Otto Heinrich Warburg as a research assistant at the Kaiser Wilhelm Institute for Biology in Dahlem, Berlin.

After four years in 1930, with 16 publications to his credit, his mentor Warburg urged him to move on and he took up the position of Assistant in the Department of Medicine at the Municipal Hospital in Altona (now part of Hamburg).

Although Germany restricted him to bringing only his personal belongings, he was fortunate that the government agents allowed him to take his equipment and research samples to England.

They proved to be pivotal to his later discoveries, especially the manometer developed by Warburg specifically for the measurement of oxygen consumption in thin slices of tissues; it was the basis for his research.

[20] He was appointed as Demonstrator in biochemistry in 1934, and in 1935 the University of Sheffield offered him a post of Lecturer in Pharmacology, with a more spacious laboratory and double the salary.

He moved with his MRC unit to the University of Oxford in 1954 as Whitley Professor of Biochemistry, the post he held until his retirement in 1967.

The editorial board of Biochemical Journal extended their good wishes on his retirement, but in return he promised to keep them busy, by producing scientific papers.

He continued his research, and took his MRC unit to the Nuffield Department of Clinical Medicine at the Radcliffe Infirmary, Oxford.

[3][27] In 1932, Krebs worked out the outlines of the urea cycle with a medical student Kurt Henseleit at the University of Freiburg.

While working at the Medical Clinic of the University of Freiburg, Krebs met Kurt Henseleit, with whom he investigated the chemical process of urea formation.

In 1904, two Germans, A. Kossel and H. D. Dakin, had shown that arginine could be hydrolysed by the enzyme arginase to form ornithine and urea in inorganic reaction.

[20][31] 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.

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.

"[34] 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.

[47][48] The proceeds were used to found the Sir Hans Krebs Trust, which provides funding for doctoral students in the biomedical field and support chemists who had to flee their home countries.

[54] In 1990, the Federation of European Biochemical Societies instituted the Sir Hans Krebs Lecture and Medal, which was endowed by the Lord Rank Centre for Research.

[55][56] The Society of Friends of Hannover Medical School gives the Sir Hans Krebs Prize, which is worth 10,000 euros.

[57][58] The Biochemical Society offers Krebs Memorial Scholarship to a postgraduate (PhD) student working in biochemistry or an allied biomedical science at any British university.