L-arginine uptake and L-phosphoarginine synthesis in Trypanosoma cruzi.
A very specific L-arginine transporter showing high affinity has been characterized in Trypanosoma cruzi epimastigotes. Uptake was found to be dependent on L-arginine concentration and it was saturable. Values for maximum velocity and Km ranged between 48.1-57.5 pmol.min-1 per 3 x 10(7) cells and between 4.2-5.5 microM, respectively. The calculated activation energy and Q10 were 31.1 KJ.mol-1, and 1.7, respectively. Uptake velocity significantly increased when cells were preincubated in the absence of L-arginine. Cells retained the labeled amino acid independently of the presence or absence of exogenous L-arginine. The specificity of L-arginine uptake was demonstrated by competition assays in the presence of 80-fold molar excess of natural amino acids and several L-arginine derivatives. The highest levels of inhibition were caused by L-homoarginine, D-arginine, L-canavanine, L-ornithine, and L-citrulline. L-arginine uptake by T. cruzi epimastigotes was not affected by the presence of potassium or sodium ions in the incubation mixture or by pH changes in the range between 5.5-8.5. The major product of L-arginine uptake was characterized as phosphoarginine. Moreover, arginine kinase activity was detected in soluble extracts from T. cruzi epimastigotes.
Pereira
C A
CA
Instituto de Investigaciones en Ingeniería Genética y Biología Molecular (CONICET), Universidad de Buenos Aires, Argentina.
Alonso
G D
GD
Paveto
M C
MC
Flawiá
M M
MM
Torres
H N
HN
D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000378:metabolism*; D001122:Arginine Kinase / Q000378:metabolism; D007700:Kinetics; D009943:Organophosphorus Compounds / Q000138:chemical synthesis; D013440:Sulfides; D013696:Temperature; D014349:Trypanosoma cruzi / Q000378:metabolism*
D009943:Organophosphorus Compounds; D013440:Sulfides; C015441:phospho-L-arginine; D001120:Arginine; D001122:Arginine Kinase