Bound lectins that mimic insulin produce persistent insulin-like activities.
Short preincubation of rat adipocytes with wheat germ agglutinin, followed by removal of unbound lectin, resulted in persistent activation of lipogenesis, which lasted at least 3 h. The bound lectin also inhibited lipolysis initiated by isoproterenol 1 or 2 h after the removal of the free lectin. This property was also shared by other insulinomimetic lectins, such as Concanavalin A and wax bean agglutinin. Persistent bioactivation is the consequence of lectin adsorbed to external cell surface determinants in a permanent fashion. This fraction is not internalized, processed, or appreciably dissociated from the cells, since the addition of N-acetyl-D-glucosamine at any time after the onset of wheat germ agglutinin-induced persistent lipogenesis leads to termination. The property of producing persistent bioactivation is not shared by insulin itself, since removal of the unbound hormone results in termination of bioactivation. This study indicates the existence of externally located fat cell surface determinants, which, upon being occupied continuously, produce persistent insulin-like activities. The study also strongly supports the notion that the initial perturbation is sufficient to activate the insulin machinery system, and that internalization and processing of hormone-receptor complexes are the sole pathway for termination.
D000117:Acetylglucosamine / Q000494:pharmacology; D000273:Adipose Tissue / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D007328:Insulin / Q000494:pharmacology*; D007545:Isoproterenol / Q000494:pharmacology; D037102:Lectins / Q000494:pharmacology*; D008055:Lipids / Q000096:biosynthesis*; D008066:Lipolysis / Q000187:drug effects; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D014909:Wheat Germ Agglutinins
D007328:Insulin; D037102:Lectins; D008055:Lipids; D014909:Wheat Germ Agglutinins; D007545:Isoproterenol; D000117:Acetylglucosamine