Partial characterization of the glucose transport activity in the Golgi-rich fraction of fat cells.

The glucose transport activity solubilized from the basal and plus insulin forms of the Golgi-rich fraction of adipocytes was partially characterized, and the results were compared with those of the activity obtained from the plus insulin form of the plasma membrane-rich fraction. The transport activity was determined in a cell-free, reconstituted, system. Prior to reconstitution, the activities in the three preparations were all (a) stable at 0 degrees C for at least 4 h, but not at 37 degrees C or above; (b) most stable at pH 7-9, and (c) less stable in Tes than in Tris buffer. After reconstitution, the three activities were all (d) stable at 0 degrees C, (e) most active at pH 5.5, (f) mildly stimulated by divalent cations, (g) unaffected by insulin or 1 mM of several SH-blocking agents, (h) inhibited by heavy metal ions, 10-100 mM of monovalent salts, organic solvents, several sugar isomers, and specific sugar-transport inhibitors. The rates of D-glucose uptake by the three liposome preparations were all inhibited more strongly by 2-deoxy-D-glucose or 3-O-methyl-D-glucose than by D-glucose. These data indicate that the general properties of the glucose transport activity in the Golgi-rich fraction are similar to those of the activity in the plasma membrane-rich fraction.