|MadSci Network: Biochemistry|
I am not sure why it is found in only this part of the Krebs Cycle instead of ATP. My two best guesses are that either 1.) this is just an evolutionary artifact and there is no good reason for it, or 2.) this is an added opportunity for regulation of the cycle. If you look at many signalling pathways or other metabolic pathways like Krebs in biological systems, they often seem unnecessarily complicated. However, they usually have developed these complications in order to build in very fine and subtle controls, to be used especially in response to situations where there is some sort of stress to the system in which one component is over- or under-produced.
This may or may not be a satisfactory answer to you, Gaurishankar, but as I said, these are my best guesses!
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