Transport of L‐Proline and its Regulation in Leishmania tropica Promastigotes*

Abstract

L. tropica promastigotes transport L-proline through an active uptake system that has saturation kinetics, temperature dependence, a requirement for metabolic energy and transport against a concentration gradient. In experiments lasting 10 min, < 10% of the proline transported is incorporated into macromolecules. The remainder is largely unaltered proline with an intracellular concentration nearly 60 times that in the reaction mixture. The uptake system has a relatively broad specificity; it is competitively inhibited by D-proline, alanine, methionine, valine, azetidine-2-carboxylate, thioproline, 3,4-dehydroproline, hydroxyproline and .alpha.-aminoisobutyric acid. Pre-established intracellular proline pools exchange with external proline and compounds that compete with it for uptake. Evidence is presented that feedback inhibition and transinhibition may regulate proline uptake in this organism.