Membrane transport of sugars in cell suspensions of sugarcane: I. Evidence for sites and specificity.

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 (14)C-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 mum, respectively).