What are the real components of carbamoyl phosphate?
When studying for my BC exam, specifically pyrimidine biosynthesis, I had some difficulty tracing back the origin of the various atoms in the pyrimidic ring. Numbering from 1 to 6, starting "down" and running clockwise, I realized atoms 1, 4, 5 and 6 (respectively 1 nitrogen and 3 carbons) came from aspartate but the two leftstanding (C2 and N3) were not that easy. Some sources say C2 comes from CO2, others from HCO3-, which one is it? Is CO2 transformed into HCO3- before the reaction? And is it true that, in fact, Carbamoyl phosphate is made from HCO3- and the glutamine's amide?
Thanks in advance
John
