Evidence that insulin causes translocation of glucose transport activity to the plasma membrane from an intracellular storage site.
The glucose transport activity of fat cells was assayed in a cell-free system. The activity was solubilized and incorporated into egg-lecithin liposomes. The carrier-mediated glucose transport activity was estimated by subtracting the cytochalasin B-insensitive component from the total glucose uptake activity of the modified liposomes. When a crude microsomal preparation from fat cells was fractionated by sucrose density gradient centrifugation, two transport activities (peaks A and B) were separated. Peak A coincided with the peak of 5'-nucleotidase, a marker of the plasma membrane. Peak B appeared to coincide with the peak of UDPGal:N-acetylglucosamine galactosyltransferase, a marker of the Golgi apparatus. Peak A was considerably smaller than peak B under basal conditions. When cells were exposed to 1 nM insulin for 5 min before homogenization, the height of peak A increased whereas that of peak B decreased. Insulin had no significant effect on the galactosyltransferase activity. The Km values of glucose transport facilitated by the activities in peaks A and B were both approximately 10-15 mM. These results imply that insulin facilitates translocation of the transport activity from an intracellular storage site to the plasma membrane.
D000273:Adipose Tissue / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002474:Cell-Free System; D005947:Glucose / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism; D007328:Insulin / Q000494:pharmacology*; D007425:Intracellular Membranes / Q000378:metabolism; D007700:Kinetics; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism*; D009237:N-Acetyllactosamine Synthase / Q000378:metabolism; D051381:Rats
D002352:Carrier Proteins; D007328:Insulin; D008565:Membrane Proteins; D009237:N-Acetyllactosamine Synthase; D005947:Glucose