Uptake of selected pyrimidines by axenically grown Entamoeba histolytica.

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.