Further evidence for a role of carbohydrates in insulin binding: studies in lectin-purified receptors.
Purification of liver membrane insulin receptors on concanavalin A- and ricin I-lectin columns gave a 15-fold enrichment in the insulin binding capacity per milligram of protein. Final receptor and protein recoveries were 53 and 3.8% respectively. Lectin-purification increased the receptor affinity for insulin, as indicated by a left-ward shift in the binding competition curve and a steeper slope in the Scatchard plot. Lectin-purification increased the receptor sensitivity towards the glycosidic probes. The maximal effects of beta-galactosidase, ricin I (galactose-binding lectin) and alpha-mannosidase were markedly amplified: 80, 90 and 60% inhibition, versus 45, 40 and 15% with particulate membranes. The limulus polyphemus (LPA) and wheat germ (WGA) agglutinins (sialic acid- and N-acetyl-glucosaminyl-binding lectins) became effective in modifying the insulin binding: 45 and 80% inhibition, respectively. The effects were dose-dependent, reversed by the monosaccharide competitors (lectin effects) and unrelated to the state of receptor occupancy. These findings indicate that, within the hormone recognition area, peptide chains containing galactose, mannose and N-acetyl-glucosamine are strictly required for insulin-receptor interaction and suggest that change in the receptor affinity is related to the role of carbohydrate in insulin binding.
D000818:Animals; D002241:Carbohydrates / Q000502:physiology*; D002462:Cell Membrane / Q000378:metabolism; D006026:Glycoside Hydrolases / Q000378:metabolism; D066298:In Vitro Techniques; D007700:Kinetics; D037102:Lectins / Q000494:pharmacology; D008099:Liver / Q000378:metabolism*; D051379:Mice; D011972:Receptor, Insulin / Q000302:isolation & purification / Q000378:metabolism*
D002241:Carbohydrates; D037102:Lectins; D011972:Receptor, Insulin; D006026:Glycoside Hydrolases