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biopax3:comment |
<b>General Background</b> Pyrimidine and purine nucleotides represent fundamental compounds central to both primary metabolism and many aspects of secondary metabolism. Involved in many cellular processes, pyrimidines are considered of vital importance for growth, development and reproduction. The <i>de novo</i> biosynthesis of pyrimidine ribonucleotides gives rise to |FRAME: UMP| (UMP) from which all other pyrimidines within the cell are derived. Further phosphotransfer and nucleotide modification reactions (illustrated in this pathway) convert the monophosphate to diphosphate and triphosphate nucleotides. |FRAME: UDP| is of special importance as it serves as a glycosyl carrier in a plethora of reactions involved in many primary and secondary metabolism pathways. <b>About This Pathway</b> The pyrimidine nucleotide metabolism enclosing phosphotransfer and nucleotide modification routes appears to connect to a network of interacting metabolic pathways involved in growth and development which is not well understood. The first enzyme of the pathway, catalyzes the phosphorylation of UMP to form UDP. The conserved glycine-rich sequence GGPG(S/A)GK, a hallmark for all eukaryotic monophosphokinases, has been found of significant importance for ATP binding and enzyme catalysis. The next enzyme in the pathway, |FRAME: NUCLEOSIDE-DIP-KIN-CPLX| (NDK), catalyzes a reaction in which the terminal phosphate of a nucleoside-triphosphate is transferred to a nucleoside-diphosphate - in this case, the transfer of a phosphate from ATP to UDP, forming UTP. The enzyme has a broad substrate specificity, and is involved in the biosynthesis of several nucleoside-triphosphates, including formation of CTP from CDP. Interconversion between thymidine and cytidine nucleosides is made possible by the glutamine (or ammonia)-dependent enzyme |FRAME: CTPSYN-CPLX|.
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