title: Biochemical characterization of the glutamate transport in Trypanosoma cruzi.
abstract: The role of amino acids in trypanosomatids goes beyond protein synthesis, involving processes such as differentiation, osmoregulation and energy metabolism. The availability of the amino acids involved in those functions depends, among other things, on their transport into the cell. Here we characterize a glutamate transporter from the human protozoan parasite Trypanosoma cruzi. Kinetic data show a single saturable system with a Km of 0.30 mM and a maximum velocity of 98.34 pmoles min(-1) per 2 x 10(7) cells for epimastigotes and 20 pmoles min(-1) per 2 x 10(7) cells for trypomastigotes. Transport was not affected by parasite nutrient starvation for up to 3h. Aspartate, alanine, glutamine, asparagine, methionine, oxaloacetate and alpha-ketoglutarate competed with the substrate in 10-fold excess concentrations. Glutamate uptake was strongly dependent on pH, but not on Na+ or K+ concentrations in the extracellular medium. These data were consistent with the sensitivity of the system to the H+ ionophore carbonyl cyanide p-trifluoromethoxyphenylhydrazone, suggesting that transport is driven by H+ concentration gradient across the cytoplasmic membrane. The glutamate transport increased linearly with temperature in a range from 15 to 40 degrees C, allowing the calculation of an activation energy of 52.38 kJ/mol.
authors.affiliation: Departamento de Fisiologia, Instituto de Biociências, Universidade de São Paulo, Rua do Matão, Travessa 14 No 101, Cidade Universitária, 05508-900 São Paulo, Brazil. asilber@iq.usp.br
authors.forename: Ariel M
authors.initials: AM
authors.lastname: Silber
authors.forename: Robert L Galvez
authors.initials: RL
authors.lastname: Rojas
authors.forename: Ursula
authors.initials: U
authors.lastname: Urias
authors.forename: Walter
authors.initials: W
authors.lastname: Colli
authors.forename: Maria Júlia Manso
authors.initials: MJ
authors.lastname: Alves
mesh_terms: D027322:Amino Acid Transport System X-AG / Q000378:metabolism*; D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism; D014355:Chagas Disease / Q000469:parasitology; D018698:Glutamic Acid / Q000032:analysis / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D010274:Parasitology / Q000379:methods; D015800:Protozoan Proteins / Q000378:metabolism; D014349:Trypanosoma cruzi / Q000378:metabolism*
chemical_list: D027322:Amino Acid Transport System X-AG; D000596:Amino Acids; D015800:Protozoan Proteins; D018698:Glutamic Acid