Characterization of nucleoside uptake and transport in Entamoeba histolytica.
The uptake and transportation of purine and pyrimidine based nucleosides by trophozoites of axenically grown Entamoeba histolytica (HMI-IMSS) were studied. The trophozoites transported adenosine and its analog tubercidin (1 microM) at a significant rate but poor transportation was observed in case of uridine (about 10% relative rate), inosine (3%), thymidine (2%) and formycin B (1%). The Km for adenosine was 160 +/- 42 microM. Unlabeled nucleosides (100 microM) inhibited adenosine and tubercidin transport. Adenosine related compounds 5'-deoxyadenosine and nebularin inhibited adenosine and tubercidine transport by 50% or more. However, inosine related compounds guanosine, 3'-deoxyinosine and formycin B were less inhibitory. The pyrimidine nucleosides uridine, thymidine and cytidine were poorly inhibitory. 6-[(4 nitrobenzyl)-mercapto] purine ribonucleoside, an inhibitor of mammalian nucleoside transporter, inhibited adenosine or tubercidin transport in E. histolytica variably between 0-30% at 10 microM, but dilazep, a known inhibitor, was inactive upto 10 microM. Increase in temperature from 22 degrees C to 33 degrees C enhanced the rate of transport of adenosine 4.5 fold, tubercidin 7.3 fold and of inosine 4 fold. These findings along with the structure activity figures suggested that transport was mediated and not passive.
Das
P
P
Department of Microbiology, National Institute of Cholera and Enteric Diseases, Calcutta, India.
Das
S R
SR
Moorji
A
A
Baer
H P
HP
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D004109:Dilazep / Q000494:pharmacology; D004748:Entamoeba histolytica / Q000378:metabolism*; D009705:Nucleosides / Q000378:metabolism*; D011684:Purine Nucleosides / Q000378:metabolism; D011741:Pyrimidine Nucleosides / Q000378:metabolism; D013868:Thioinosine / Q000031:analogs & derivatives / Q000494:pharmacology
D009705:Nucleosides; D011684:Purine Nucleosides; D011741:Pyrimidine Nucleosides; D013868:Thioinosine; D004109:Dilazep; C001789:4-nitrobenzylthioinosine