Studies on the transport of carbohydrate in Crithidia luciliae.

Abstract

AbstractThe entrance of carbohydrates into the cells of C. luciliae has been studied, using the non‐utilizable monosaccharides: L‐sorbose, D‐xylose, L‐xylose, D‐arabinose, L‐arabinose, L‐rhamnose, D‐lyxose, D‐2‐deoxyglucose, and L‐fucose; all nine sugars entered the cell. At 0.5 mM external concentration the rate of increase in intracellular concentration is constant for all sugars until the intracellular concentrations equal or exceed the extracellular concentration. At 20 mM external concentration, the rate of increase of intracellular concentration decreases continuously and the maximum intracellular concentration never exceeds the extracellular concentration. There is competition between monosaccharides presented simultaneously to the cells and the transport mechanism shows enormously greater affinity for glucose than for other monosaccharides. The rate of carbohydrate entrance is inhibited 50% and 70% by KCN(10−4 M) and DNP(10−5 M) respectively at 0.5 mM external concentrations. However, these inhibitors do not affect transport from external concentrations of the order of 0.02 M. These data are interpreted as indicating two mechanisms for carbohydrate entrance: (a) an active transport mechanism, active at low external concentration and dependent upon a supply of metabolic energy; (b) facilitated diffusion, of importance only at high external concentrations. These results are compared with those reported in the literature for other types of cells.