STUDY OF ANALOGS OF THYMIDINE-5'-MONOPHOSPHATE AND THYMIDINE AS SUBSTRATES OR INHIBITORS OF CHICK-EMBRYO LIVER THYMIDYLATE KINASE

The phosphorylation of thymidine-5'-monophosphate (dTMP) by chick embr yo liver thymidylate kinase (Km (dTMP) = 1.2 mu M) was inhibited by th e 5'-monophosphate derivatives of 5-bromo-2'-deoxyuridine (5-Br-dUMP), 5-iodo-2'-deoxyuridine (5-I-dUMP), 2',3'-dideoxythymidine (ddTMP), 3' -azido-3'-deoxythymidine (AZT-MP) and the methylene phosphonate analog ue of AZT-MP with IC50 values of 8, 24, 14, 5 and 6 mu M respectively. 5-Fluoro-2'-deoxyuridine (5-F-dUMP) and dUMP were poor inhibitors (IC 50 values > 300 mu M). 5-Br-dUMP and 5-I-dUMP were found to be signifi cant substrates of thymidylate kinase with phosphorylation efficiencie s (Vmax/Km) of 26 and 6% of that of dTMP, respectively. In contrast, A ZT-MP and ddTMP were poor substrates, being phosphorylated 800-fold le ss efficiently than dTMP. Thymidylate kinase was also significantly in hibited by thymidine and AZT. Our data give a better insight into the topology of the dTMP binding site of this enzyme and show that the 3'- hydroxyl group of dTMP plays a critical role in catalysis.