UPTAKE AND TURNOVER OF GLUCOSE IN LEISHMANIA-DONOVANI

Glucose uptake and metabolism by Leishmania donovani promastigotes was studied using D-[C-14]glucose in combination with the silicone oil ce ntrifugation technique on organisms preadapted to different growth rat es and glucose availability in the chemostat. The uptake step was diff erentiated 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 concentrati on on cells grown at high or low growth rate with glucose either as gr owth rate-limiting substrate, or present in excess. Glucose uptake as a function of its external concentration could be described as consist ing of two components (1) a rapid equilibration owing to facilitated d iffusion, followed by (2) a much slower uptake that involves an enzyma tic 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 experimen ts indicate that the active uptake of glucose by L. donovani, as repor ted by others does not occur across the plasma membrane and should be reinterpreted as the intracellular conversion of glucose into metaboli tes and storage carbohydrate.