- The sentrin-conjugating enzyme mUbc9 interacts with GLUT4 and GLUT1 glucose transporters and regulates transporter levels in skeletal muscle cells. Giorgino, F., de Robertis, O., Laviola, L., Montrone, C., Perrini, S., McCowen, K.C., Smith, R.J. Proc. Natl. Acad. Sci. U.S.A. (2000)