Aerobic and Anaerobic Uptake of Sugars in Schizosaccharomyces pombe

SUMMARY: Aerobic cells of the yeast Schizosaccharomyces pombe accumulated 2-deoxy-d-glucose (2-DOG) and glucosamine, but were unable to accumulate 3-O-methyl-d-glucose, 6-deoxy-d-glucose, d-xylose and d-arabinose. Uptake of all sugars tested displayed saturation kinetics; however, only 2-DOG, glucosamine and d-glucose exhibited mutual competitive inhibition of uptake and the phenomenon of exchange transport. Thus, they share a common ‘glucose transport system’. Uncouplers inhibited sugar accumulation or induced sugar outflow from preloaded cells. The uptake of sugars of the glucose transport system was pH dependent and was accompanied by a stoicheiometric cotransport of H+. Since millimolar concentrations of the lipophilic cation tetraphenylphosphonium (which depolarizes the membrane potential) prevented sugar accumulation, the transport was electrogenic. Thus, the glucose carrier is a H+-symporter. Accumulation of sugars was inhibited by the plasma membrane ATPase inhibitors Dio-9 and N, N’-dicyclohexylcarbodiimide. Anaerobic cells of S. pombe were virtually unable to transport 2-DOG and glucosamine. However, when energized by glucose, the accumulation of both sugars was completely restored. This anaerobic transport was also catalysed by the glucose carrier.