Uptake and turnover of glucose in Leishmania donovani

Glucose uptake and metabolism by Leishmania donovani promastigotes was studied using D-[14C]glucose in combination with the silicone oil centrifugation technique on organisms preadapted to different growth rates and glucose availability in the chemostat. The uptake step was differentiated from the subsequent metabolism by separation in time rather than by using non-metabolisable analogues. The uptake of glucose was measured as a function of time and/or the external glucose concentration on cells grown at high or low growth rate with glucose either as growth rate-limiting substrate, or present in excess. Glucose uptake as a function of its external concentration could be described as consisting of two components (1) a rapid equilibration owing to facilitated diffusion, followed by (2) a much slower uptake that involves an enzymatic component. This slower accumulation of label could be explained as the conversion of glucose into metabolites and a storage carbohydrate. Uptake experiments in the presence of inhibitors indicated that the conversion of glucose was an energy dependent process. These experiments indicate that the active uptake of glucose by L. donovani, as reported by others does not occur across the plasma membrane and should be reinterpreted as the intracellular conversion of glucose into metabolites and storage carbohydrate.