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Biochim Biophys Acta. 1992 Aug 24;1109(2):172-8.

Identification of a broad-specificity nucleoside transporter with affinity for the sugar moiety in Giardia intestinalis trophozoites.

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  • 1Department of Microbiology and Immunology, University of Adelaide, Australia.


A broad-specificity nucleoside transporter has been identified in Giardia intestinalis trophozoites, using a rapid sampling assay to measure influx of [3H]deoxycytidine, [3H]adenosine and [3H]guanosine at 0 degrees C. The influx of each labelled nucleoside was inhibited strongly by all common, naturally-occurring nucleosides but only poorly or not at all by nucleobases, indicating that the transporter recognizes structural features on the furanosyl moiety of ribo- and 2'-deoxyribonucleosides. Both 2'- and 5'-deoxyadenosine were potent inhibitors of influx (greater than 95% inhibition at 2 mM), whereas 3'-deoxyadenosine was significantly less effective (approx. 70% inhibition), and 2',3'-dideoxycytidine and cytosine arabinoside were virtually inactive (0-20% inhibition). The data reveal that the 2'- and 5'-hydroxyl groups are not necessary for the recognition of nucleosides by this transporter. However, the 3'-hydroxyl appears to be important. Michaelis-Menten constants (Km) were calculated for the influx at 0 degrees C of deoxycytidine (220 +/- 116 microM) and adenosine (45 +/- 24 microM), with respective Vmax values of 13 +/- 4 and 11 +/- 2 pmol min-1 (10(6) cells)-1. Only 12-26% of [3H]thymidine influx occurred through this transporter, the remainder entering the cells through a thymine/uracil-specific transporter described previously. Thymidine exhibited a Ki of 205 +/- 90 microM against [3H]deoxycytidine influx.

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