Hp. De Koning et Sm. Jarvis, A highly selective, high-affinity transporter for uracil in Trypanosoma brucei brucei: evidence for proton-dependent transport, BIOC CELL B, 76(5), 1998, pp. 853-858
Citations number
19
Categorie Soggetti
Cell & Developmental Biology
Journal title
BIOCHEMISTRY AND CELL BIOLOGY-BIOCHIMIE ET BIOLOGIE CELLULAIRE
The presence of an uptake mechanism for uracil in procyclic forms of the pr
otozoan parasite Trypanosoma brucei brucei was investigated. Uptake of [H-3
]uracil at 22 degrees C was rapid and saturable and appeared to be mediated
by a single high-affinity transporter, designated U1, with an apparent K-m
of 0.46 +/- 0.09 mu M and a V-max of 0.65 +/- 0.08 pmol.(10(7) cells)(-1)
s(-1). [H-3]Uracil uptake was not inhibited by a broad range of purine and
pyrimidine nucleosides and nucleobases (concentrations up to 1 mM), with th
e exception of uridine, which acted as an apparent weak inhibitor (K-i valu
e of 48 +/- 15 mu M). Similarly, most chemical analogues of uracil, such as
5-chlorouracil, 3-deazauracil, and 2-thiouracil, had little or no affinity
for the U1 carrier. Only 5-fluorouracil was found to be a relatively poten
t inhibitor of uracil uptake (K-i = 3.2 +/- 0.4 mu M). Transport of uracil
was independent of extracellular sodium and potassium gradients, as replace
ment of NaCl in the assay buffer by N-methyl-D-glucamine, KCl, LiCl, CsCl,
or RbCl did not affect initial rates of transport. However, the proton iono
phore carbonyl cyanide chlorophenylhydrazone inhibited up to 70% of [H-3]ur
acil flux. These data show that uracil uptake in T. b. brucei procyclics is
mediated by a single high-affinity transporter with high substrate selecti
vity and are consistent with a nucleobase-H+-symporter model for this carri
er.