'Abnormality of 2-deoxyglucose uptake kinetics in fibroblasts at low concentrations

2-deoxyglucose uptake rates at low sugar concentrations (less than 500 microM) appeared to be lower than those predicted by the Michaelis-Menten model which correctly described higher concentrations. This phenomenon which we will call concentration-dependent transport lag, was also observed for L-glucose uptake which suggest that this phenomenon is carrier-independent. A model involving the perimembrane space is developed which, for L-glucose, gives k1 = 0.931 +/- 0.072 X 10(-6) l X mg protein-1 X minute-1, k2 = 2.97 +/- 0.19 X 10(-7) l X mg protein-1 X minute-1 and So = 88,8 +/- 4,3 microM; where k1 is the diffusion constant in the cell membrane, k2 is the diffusion constant in the perimembrane space and So the sugar concentration required in the external medium in order to provide an équivalent sugar concentration in the transport carrier area.