Editing Hans Krebs (biochemist) (section)

=== Urea cycle (Krebs–Henseleit cycle) ===
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.<ref>{{cite journal|last1=Kinne-Saffran|first1=E|last2=Kinne|first2=RK|title=Vitalism and synthesis of urea. From Friedrich Wöhler to Hans A. Krebs|journal=American Journal of Nephrology|year=1999|volume=19|issue=2|pages=290–294|pmid=10213830|doi=10.1159/000013463|s2cid=71727190}}</ref> Based on this reaction, Krebs and Henseleit postulated that in living cells, similar reaction could occur, and that ornithine and [[citrulline]] could be the intermediate reactions.<ref>{{cite book|last1=Graßhoff|first1=Gerd|last2=May|first2=Michael|editor1-last=Holmes|editor1-first=Frederic L.|editor2-last=Renn|editor2-first=Jürgen|editor3-last=Rheinberger|editor3-link=Hans-Jörg Rheinberger|editor3-first=Hans-Jörg|title=Reworking the Bench : Research Notebooks in the History of Science|year=2003|publisher=Kluwer Academic Publishers|location=Dordrecht|isbn=978-1-4020-1039-2|pages=269–294|doi=10.1007/0-306-48152-9_13|chapter=Hans Krebs' and Kurt Henseleit's Laboratory Notebooks and Their Discovery of the Urea Cycle-Reconstructed with Computer Models}}</ref><ref>{{cite book|last1=Nickelsen|first1=Kärin|author1-link= Kärin Nickelsen |last2=Graßhoff|first2=Gerd|editor1-last=Hon|editor1-first=Giora|editor2-last=Schickore|editor2-first=Jutta|editor3-last=Steinle|editor3-first=Friedrich|title=Going Amiss in Experimental Research|year=2009|publisher=Springer Verlag|location=Dordrect, Netherlands|isbn=978-1-4020-8892-6|pages=91–117|doi=10.1007/978-1-4020-8893-3_7}}</ref> Krebs started working on the possible method for the synthesis of arginine. Using his Warburg manometer, he mixed a slice of liver with purified ornithine and citrulline. He found that citrulline acted as a [[catalyst]] in the metabolic reactions of urea from [[ammonia]] and [[carbon dioxide]]. He and Henseleit published their discovery in 1932. Thus the [[urea cycle]] (or "ornithine cycle") was established, and it was the first metabolic cycle to be discovered.<ref name=wilson/><ref>{{cite journal|last1=Holmes|first1=FL|title=Hans Krebs and the discovery of the ornithine cycle|journal=Federation Proceedings|year=1980|volume=39|issue=2|pages=216–25|pmid=6986292}}</ref>