title: Uptake of selected pyrimidines by axenically grown Entamoeba histolytica.
abstract: This study was conducted to determine the mode(s) of uptake of selected pyrimidine bases and nucleosides by axenically grown Entamoeba histolytica. Two-minute uptake studies with 3H-labeled compounds showed the following: 1) uridine and cytidine are taken up, in part, by a carrier mediated system; 2) uracil, cytosine, thymine and thymidine enter amebae via passive diffusion; both cytidine and uridine are taken up by passive diffusion when present at exogenous concentration greater than 500 muM; 3) specific carrier sites are used for transport of uridine-cytidine and uridine-adenosine; 4) cytidine and uridine uptake is markedly inhibited by iodoacetate and N-ethylmalemide; 5) hypoxanthine (10mM) stimulates uptake of uridine; 6) ribose fails to inhibit uptake of cytidine and uridine; 7) cytidine uptake exceeds that of uridine (i.e., apparent Vmax for: a) cytidine = 10.0 nmoles/2 min/10(6) amebae; b) uridine = 3.0 nmoles/2 min/10(6) amebae); 8) Kt for: cytidine = 0.30 mM; uridine = 0.21 mM; 9) Q 10's at 35.5 C vs 25.5 C for: a) cytidine = 3.9; b) uridine = 2.6.
mesh_terms: D000818:Animals; D001692:Biological Transport; D003470:Culture Media; D004748:Entamoeba histolytica / Q000254:growth & development / Q000378:metabolism*; D007700:Kinetics; D011741:Pyrimidine Nucleosides / Q000378:metabolism*; D011744:Pyrimidinones / Q000378:metabolism*; D011955:Receptors, Drug; D012266:Ribose / Q000494:pharmacology; D013997:Time Factors
chemical_list: D003470:Culture Media; D011741:Pyrimidine Nucleosides; D011744:Pyrimidinones; D011955:Receptors, Drug; D012266:Ribose