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Membrane Transport of Sugars in Cell Suspensions of Sugarcane

I. Evidence for Sites and Specificity ^1,2

^a Department of Physiology and Biochemistry, Experiment Station, Hawaiian Sugar Planters' Association, Honolulu, Hawaii 96822

Sugar uptake by sugarcane cells in suspension culture was measured over short incubation time spans (5 seconds to 4 minutes), and membrane transport rates were calculated. A relatively high proportion of labeled products in cell extracts after incubation of cells with ¹⁴C-glucose for 5 seconds was sugar phosphates (56%); fructose and sucrose began to appear after 15 and 30 seconds, respectively. Galactose and 3-O-methylglucose competed appreciably with glucose uptake, but ketohexoses and pentoses did not; there was no detectable uptake of sucrose. It is postulated that besides endogenous phosphorylation and further metabolism of glucose the configuration of the hydroxyl on the carbon-2 may be important for efficient membrane transport. The cells had a particularly high affinity for glucose and 3-O-methylglucose (Km = 15 and 16 µM, respectively).

² This investigation was supported in part with funds provided by the United States Department of Agriculture agreement No. 12-14-100-10430(34) to the Experiment Station of the Hawaiian Sugar Planters' Association.