Nucleotide 2 -deoxycytidine monophosphate

Describe a nucleotide. Draw the structural formula for deoxycytidine monophosphate, analogous to deoxy-adenylic acid, in which cytosine is the organic base. 

While mammahan cells reutilize few free pyrimidines, salvage reactions convert the ribonucleosides uridine and cytidine and the deoxyribonucleosides thymidine and deoxycytidine to their respective nucleotides. ATP-dependent phosphoryltransferases (kinases) catalyze the phosphorylation of the nucleoside diphosphates 2 "-de-oxycytidine, 2 -deoxyguanosine, and 2 -deoxyadenosine to their corresponding nucleoside triphosphates. In addition, orotate phosphoribosyltransferase (reaction 5, Figure 34-7), an enzyme of pyrimidine nucleotide synthesis, salvages orotic acid by converting it to orotidine monophosphate (OMP). 

Nucleoside kinases are a class of enzymes that catalyze the phosphorylation of nucleosides to make nucleoside monophosphates (Figure 22.2) as part of nucleotide biosynthetic salvage pathways. ATP provides the energy and phosphate for the reaction. Example enzymes include thymidine kinase, deoxycytidine kinase, and deoxyguanosine kinase. 

When phosphoric acid is esterified to one of the hydroxyl groups of the sugar portion of a nucleoside, a nucleotide is formed (Figure 9.4). A nucleotide is named for the parent nucleoside, with the suffix -monophosphate added the position of the phosphate ester is specified by the number of the carbon atom at the hydroxyl group to which it is esterified—for instance, adenosine 3 -monophosphate or deoxycytidine 5 -monophosphate. 

The kinase which converts deoxycytidine to its 5 -monophosphate has been studied most extensively in preparations from calf thymus 35, 36). The preferred substrate is deoxycytidine, for which the Michaelis constant (5 X 10 M) is much lower than that of two other substrates, deoxyadenosine and deoxyguanosine. Cytidine, uridine, and thymidine are not phosphorylated by this enzyme. Deoxycytidine kinase is subject to a complex pattern of allosteric regulation by nucleotides. The end product of deoxycytidine phosphorylation, dCTP, is a potent inhibitor this inhibition is reversed by dTTP. The enzyme has a rather broad specificity for the phosphate donor, with the triphosphates of the natural ribo- and deoxyribonucleosides being substrates the inactivity of dCTP is a notable exception. 

Among the frequently studied DNA components are nucleotides and nucleosides. A number of the DNA-like conformations of the isolated nucleotides have been revealed. The S/anti conformation is the most favorable for 2 -deo thymi-dine monophosphate (mTMP), 2 -deoxycytidine (mCMP), and 2 -deoxyadenosine (mAMP) S/syn conformation is favorable for 2 -monophosphate deoxyguanosine (mGMP). Coirformers with the syn orientation of nucleobase, relative to the sugar moiety, exist only in the case of mGMP. However, conformers with an orthogonal orientation of the nucleobase relative to the sugar moiety are found in mCMP mAMP molecules. 

An enzyme partially purified from yeast acts upon the nucleotides of adenine, guanine, and uridine to carry out transphosphorylation (Eqs. 33) to 36)] 112-116). Nucleoside monophosphate kinases have been partially purified from E. coli, which catalyzes the formation of triphosphates of deoxyadenine, deoxyguanosine, thymidine, and deoxycytidine from their corresponding 5 -monophosphates, in the presence of ATP 116, 117). 

Figure 2 UV spectra of the DNA nucleotides deoxyadenosine 5 -monophosphate (A), deoxyguanosine 5 -monophosphate (G), deoxycytidine 5 -monophosphate (C) and thymidine 5 -mono-phosphate (T). The spectrum of uracil Is almost Indistinguishable from that of thymine.

---