[MJF]

I know before the urea cycle begins, an amino acid has to go through a reaction to free up NH3.

In the case of glutamate, does it matter if it is either glutamate or its ionic form, glutamic acid? Different sources are telling me that it is one or the other.

Different sources are also telling me that either CO2 or HCO3- are used in the urea cycle to form carbamoyl phosphate. Is it ok to use both or is it one and not the other?

[Babcock_Hall]

With respect to the first question, suppose that I asked you what is the most abundant ionic form of glutamic acid in a cell.  What would you say?

Carboxylase enzymes either use CO₂ or they use bicarbonate.  RUBISCO is an example of the former, and pyruvate carboxylase is an example of the latter.  What are your sources of information, and how trustworthy do you think that they are.