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Mol Membr Biol. 1995 Jul-Sep;12(3):263-9.

Characterization of the intracellular GLUT-4 compartment.

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Department of Cell Biology and Physiology, Washington University School of Medicine, St Louis, MO, USA.


Insulin stimulates glucose transport in muscle and adipose tissue by triggering the translocation of the glucose transporter GLUT-4 from intracellular vesicles to the cell surface. In the present study we have attempted to characterize the intracellular GLUT-4 compartment using vesicle immunoadsorption. Silver staining of this fraction indicates that this compartment contains numerous polypeptides that exhibit a marked change in mobility upon treatment with reducing agents. The polypeptide composition of GLUT-4-containing vesicles isolated from a variety of insulin-sensitive cell types, including heart, adipose tissue, skeletal muscle and 3T3-L1 adipocytes, is similar. In addition, the polypeptide composition of the GLUT-4 compartment isolated from CHO cells transfected with GLUT-4 resembles that observed in insulin-sensitive cells. Two major proteins in this vesicle fraction isolated from all cell types are the transferrin receptor (TfR) and the mannose 6-phosphate/IGF II receptor (MPR). Furthermore, vesicles immunoadsorbed from adipocytes, with antibodies specific for GLUT-4 and the TfR, also show conservation in their overall polypeptide composition. Protein micro sequencing of a major 80 kDa polypeptide enriched in the GLUT-4 compartment isolated from skeletal muscle revealed this protein to be rat transferrin. These data indicate that there is a close relationship between the intracellular GLUT-4 compartment and the endosomal system. Future studies will be required to determine if it is possible to isolate subcompartments within this system to determine if GLUT-4 is targeted to a specialized secretory compartment in insulin-sensitive cells or simply a subdomain within recycling endosomes.

[Indexed for MEDLINE]

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