Synthesis of Pyrimidine Ribonucleotides
Biosynthesis of Purine Nucleotides, Pyrimidine …
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Purine Nucleotide | Nucleotides | Biosynthesis - Scribd
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The Synthesis and Degradation of Nucleotides
FIGURE 16–4 (a) De novo synthesis of pyrimidine nucleotides: biosynthesisof UTP and CTP via orotidylate. The pyrimidine is constructed from carbamoylphosphate and aspartate. The ribose 5-phosphate is then added to the completedpyrimidine ring by orotate phosphoribosyltransferase. The first step in thispathway (not shown here; is the synthesis of carbamoyl phosphate from CO2and NH4+, catalyzed in eukaryotes by carbamoyl phosphate synthetase II. (b)Channeling of intermediates in bacterial carbamoyl phosphate synthetase.(Derived from PDB ID 1M6V.) The large and small subunits are shown in gray andblue, respectively; the channel between active sites (almost 100 Å long) isshown as a yellow mesh. A glutamine molecule (green) binds to the small subunit,donating its amido nitrogen as NH4+ in a glutamine amidotransferase–typereaction. The NH4+ enters the channel, which takes it to a second active site,where it combines with bicarbonate in a reaction requiring ATP (bound ADP inblue). The carbamate then reenters the channel to reach the third active site,where it is phosphorylated to carbamoyl phosphate (bound ADP in red).