2 -Deoxycytidine 5 ’ -monophosphate complexes

An example is given in Fig. 1, where normalized total fluorescence decays are shown for 2 -deoxynucleosides and 2 -deoxynucleotides. In contrast to previous findings our work revealed that the fluorescence decays are complex and cannot be described by single exponentials. They consist of an ultrafast component (< 200 fs) and a slower one (ranging from about 0.4 ps for 2 -deoxyadenosine up to 1.4 ps in the case of 2 -deoxycytidine 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. 

There are three levels of complexity. At the lowest level, there are four bases two purines (adenine [A] and guanine [G]) and two pyrimidines (thymine [T] and c osine [C]). At the next level, each of these is attached to the anomeric carbon of 2-deoxyribose, and they are now called deoxyribonucleosides and their names are deoxyadenosine, deoxyguanosine, deoxythymidine, and deoxycytidine. The addition of phosphate esters at C5 of the deoxyribose units changes the name to deoxyribonucleotide,for example, deoxyadenosine 5 -monophosphate. 

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