Urea cycle discovery

A medical historian reconstructs the events leading to the discovery of the urea cycle. 

The fumarate released in the urea cycle links the urea cycle with the TCA cycle. This fumarate is hydrated to malate, which is oxidized to oxaloacetate. The carbons of oxaloacetate can stay in the TCA cycle by condensation with acetyl-CoA to form citrate, or they can leave the TCA cycle either by gluconeogenesis to form glucose or by transamination to form aspartate as shown in figure 22.9. Because Krebs was involved in the discoveries of both the urea cycle and the TCA cycle, the interaction between the two cycles shown in figure 22.9 is sometimes referred to as the Krebs bicycle. 

At the University of Freiburg (1932), he discovered a series of chemical reactions (now known as the urea cycle) by which ammonia is converted to urea in mammalian tissue. For his discoveries of chemical reactions in living organisms now known as the citric acid or Krebs cycle, he was awarded the 1953 Nobel Prize for physiology or medicine. These reactions involve the... 

Discovery of the ornithine or urea cycle (Krebs and Henseleit)... 

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