CTP Synthase (Sarah Pyfrom)
CTP synthase (synthetase)
Figure 1. 3D model of human CTP synthase.
Biological process: pyrimidine biosynthesis.
Molecular function: converts UTP to CTP.
Cellular component: ???
Cytidine 5'-triphosphate (CTP) synthase uses either ammonia or L-glutamine as the source of nitrogen in order to transform UTP into CTP. MacDonnell JE, Lunn FA, Bearne SL.
Figure 2. Conversion of UTP to CTP by CTP synthase using the NH2 group from Glutamine and ATP as the activator. CTP synthase is activated by either GTP or ATP, converting them into ADP or GDP respectively. A (adenine) and G (guanine) are both purines. By deconstructing a purine in order to form a pyrimidine, CTP synthase can affect the balance of purines to pyrimidines.
Even though ATP is required for synthesis of CTP by CTP synthase, I found an article that suggests that GTP is also necessary as an allosteric moderator when glutamine is used as the substrate.MacDonnell JE, Lunn FA, Bearne SL. However, I have found no other evidence that GTP is necessary for CTP synthase to use glutamine as a substrate. Although, I have found other papers which agree that CTP synthase can use either ATP or GTP to power the conversion of UTP to CTP.
Functions of CTP synthase:
CTP synthase is necessary for all life, and is involved in the formation of ATP from ADP source. It has been shown that ratios of UTP:CTP can control or regulate other enzymes such as ATCase. GA O'Donovan, S Herlick, DE Beck, PK Dutta CTP synthase is negatively affected by increased levels of CTP. In this way, the pathway moderates itself by creating a negative feedback loop. CTP synthase is activated by the presence of its substrates: ATP and UTP.
BLASTp hits confirm that high identity is found between CTP synthases in many other species and Halomicrobium mukohataei.
The GC content of this gene is 63.8% which is quite similar to our species' average of 65%. This suggests that the gene is not "alien" to our species' genome.
In humans, high levels of CTP synthase have been found in several cancer cells. Cyclopentenyl cytosine, acivicin and 3-deazauridine are all CTP synthase inhibitors that can halt or inhibit the progression of some cancer cells.