Further characterization of the insulin receptor glycosidic moiety in rat adipocytes

Abstract

Simultaneous or sequential treatment of rat adipocytes with neuraminidase plus β-galactosidase decreased insulin binding by 43%. No modification was observed with either enzyme individually. α-Mannosidase enhanced insulin binding (38%), whereas β- N-acetylglucosaminidase and α- l-fucosidase were ineffective. Lectins that interact with galactose ( Ricinus communis I, RCA I), mannose, Lens culinaris agglutinin (LCA), Concanavalin A (Con A) or N-acetylglucosamine (wheat-germ agglutinin, WGA) decreased insulin binding by 43, 57, 59 and 85% respectively. Lectin inhibition was dosedependent, saturable and prevented by specific monosaccharides. RCA I, LCA, Con A and WGA decreased the insulin dissociation process by 45, 90, 78 and 84% respectively. Lectins specific for sialic acid, terminal galactose, N-acetylgalactosamine or fucose ( Limulus polyphemus, peanut, soybean and Ulex I agglutinins) did not modify either insulin binding or dissociation. These results indicate involvement of penultimate d-galactose, internal N-acetyl- d-glucosamine and d-mannose residues in both processes. They suggest that, in rat adipocytes, a glycosidic moiety participates in the insulin-receptor interaction through N-linked oligosaccharides of the ‘complex type’.