TRICHOMONAS-VAGINALIS THYMIDINE KINASE - PURIFICATION, CHARACTERIZATION AND SEARCH FOR INHIBITORS

We report that a thymidine kinase (TK) activity is present in Trichomo nas vaginalis and can be separated from the deoxyribonucleoside phosph otransferase. T. vaginalis TK, purified 11200-fold to apparent homogen eity, has a molecular mass of 31500 Da. It phosphorylates not only thy midine (K-m 0.18 mu M) but also deoxycytidine (K-m 0.88 mu M) and deox yuridine (K-m 0.14 mu M). In contrast with T. vaginalis deoxyribonucle oside phosphotransferase, the TK activity is strongly inhibited by nov el deoxyuridine analogues such as 5-methyl-4'-thio-2'-deoxyuridine (MT dU) (K-i 20 nM) and 5-iodo-4'-thio-2'-deoxyuridine (ITdU) (K-i 24 nM). MTdU and ITdU are phosphorylated by T. vaginalis TK in vitro. In vivo they inhibit [H-3]thymidine incorporation in T. vaginalis cultured ce lls and T. vaginalis growth (IC50 7.5 and 24 mu M respectively; minima l lethal dose 100 mu M). Thus the TK inhibitors described here demonst rate the key role of T. vaginalis TK for protozoal growth and viabilit y and indicate TK as a new target for the design of antitrichomonal dr ugs.