Fig. 2.

Nucleoside salvage pathway for the production of 2′-deoxynucleoside triphosphates. Scavenged 2′-deoxynucleosides are imported by designated membrane transporter proteins and serve as substrate for dNK. Alternatively, cleavage of the nucleobase by phosphorylase feds into other pyrimidine and purine metabolism pathways. Separately, thymidylate synthase and ribonucleotide reductase catalyze the final reactions of the nucleotide de novo pathways, producing TMP and dNDPs which are converted to their triphosphates by dNMPK and NDPK. dNK = 2′-deoxynucleoside kinase, dNMPK = 2′-deoxynucleoside monophosphate kinase, NDPK = nucleoside diphosphate kinase