Characterization of a major protein in GLUT4 vesicles. Concentration in the vesicles and insulin-stimulated translocation to the plasma membrane.

GLUT4-enriched vesicles from fat and muscle cells contain a major protein of 165 kDa. In the present study we have prepared GLUT4 vesicles from a large number of rat adipocytes, isolated the 165-kDa protein by SDS-gel electrophoresis, and obtained the sequences of four tryptic peptides. Comparison of the sequences with those in protein data banks showed that the 165-kDa protein had not previously been sequenced. An antibody preparation against one of the peptides immunoblotted the 165-kDa protein. By this means it was found that the 165-kDa protein was concentrated in GLUT4 vesicles, and that insulin treatment of rat adipocytes caused a translocation of the protein to the plasma membrane that paralleled the translocation of GLUT4.