Broad specificity hexose transport system with differential mobility of loaded and empty carrier, but directional symmetry, is common property of mammalian cell lines.
Rapid kinetic techniques were employed to measure the transport of the nonmetabolizable hexose, 3-O-methyl-D-glucose, in suspensions of human HeLa cells, mouse L- and P388 leukemia cells, and Chinese hamster ovary cells in zero-trans entry and exit and equilibrium exchange procedures. The kinetic parameters of transport were computed by fitting appropriate integrated rate equations to time courses of transmembrane equilibration of radiolabeled substrate. Transport of all four lines, as in Novikoff rat hepatoma cells, conformed to a simple carrier model with directional symmetry but differential mobility of loaded and empty carrier. As was apparent from a comparison of influx and exchange flux, the loaded carrier of all cell types moved between 4 and 14 times faster than the empty carrier. ATP depletion of the cells by incubation in glucose-free medium containing KCN and iodoacetate had no significant effect on the kinetic properties of the transporter. ATP-depleted cells were used to measure the transport of D-glucose, 2-deoxyglucose, D-galactose, and D-glucosamine in the absence of intracellular metabolism. The differential mobilities of empty carrier and carrier loaded with these hexoses and the efficiency of their transport were equivalent to those observed with 3-O-methylglucose, but the Michaelis-Menten constants for the transport of D-galactose and D-glucosamine were 5-8-fold higher than those for D-glucose, 2-deoxy-D-glucose, and 3-O-methylglucose, which were about equivalent.
D000818:Animals; D001693:Biological Transport, Active; D002352:Carrier Proteins / Q000378:metabolism*; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus; D005260:Female; D006367:HeLa Cells / Q000378:metabolism; D006601:Hexoses / Q000378:metabolism*; D007700:Kinetics; D007739:L Cells / Q000378:metabolism; D007941:Leukemia P388 / Q000378:metabolism; D008114:Liver Neoplasms, Experimental / Q000378:metabolism; D008757:Methylglucosides / Q000378:metabolism*; D008759:Methylglycosides / Q000378:metabolism*; D051379:Mice; D010053:Ovary; D051381:Rats
D002352:Carrier Proteins; D006601:Hexoses; D008757:Methylglucosides; D008759:Methylglycosides