Stereospecific d-glucose transport in mixed membrane and plasma membrane vesicles derived from cultured chick embryo fibroblasts

Abstract

Mixed membrane vesicles prepared from cultured chick embryo fibroblasts possess a stereospecific d-glucose transport system, the properties of which are identical to those of the system in intact cells. Uptake of d-glucose proceeds without chemical alteration. The rate of stereospecific uptake of d-glucose into the mixed vesicles is 70% greater than that of the homogenate and uptake is directly proportional to membrane protein concentration. Stereospecific d-glucose uptake appears linear for 0.3 min, reaches a maximum at 2–5 min, and declines to zero by 5 h as l-glucose enters the vesicles. Uptake is osmotically sensitive and inhibited by cytochalasin B ( K i = 0.13 μM) and the structural analogues of d-glucose : d-mannose, 2-deoxy- d-glucose, 3- O- methyl- d- glucose , d-galactose and maltose, but not by sucrose or l-glucose. Uphill counterflow can be demonstrated and the apparent activation energy displays a transition from 47.7 kcal/mol below 11°C to 18.1 kcal/mol above 11°C. Stereo-specific uptake rates of mixed vesicles prepared from Rous sarcoma virus-transformed cells are increased 30% over control values, and are increased 66% in vesicles derived from cells incubated for 24 h in glucose-free medium. Plasma membrane vesicles prepared from these cells by a dextran cushion centrifugation procedure display a 9-fold increase in the specific activity of stereospecific d-glucose uptake relative to the homogenate. Extraction of these membranes with dimethylmaleic anhydride (5 mg/mg protein) results in substantial or complete removal of major polypeptides of molecular weight 40 000, 55 000, 75 000, 78 000 and 200 000 with no loss in total uptake activity. Following extraction, major polypeptides of molecular weight 28 000, 33 000 and 68 000 remain in the membrane residue.