摘要：

Insulin receptors from human placenta and from cultured lymphocytes (IM-9 line) were solubilized in Triton X-100 and applied to agarose columns containing 12 different immobilized lectins. Receptors from both tissues were adsorbed by lectins that bind N-acetylglucosamine (wheat germ), mannose (concanavalin A, lentil, and pea), and galactose (ricins I and II) but were unretained by lectins that bind N-acetylgalactosamine (horse gram, S. Japonica, and soybean), fucose (gorse seed I), and galactose (B. simplicifolia and peanut). After desorption with the appropriate monosaccharides, the insulin-binding capacity of the receptor was increased between 5- and 50-fold with recoveries ranging from 7% to 98%. However, when the solubilized membranes from both tissues were chromatographed sequentially on three different lectin columns (e.g., wheat germ, lentil, and ricin I), the receptor showed only a minor increase in purity after elution from the second and third columns. Receptors for multiplication-stimulating activity (MSA) and epidermal growth factor (EGF) in the solubilized placental membranes behaved very similarly to insulin receptors on sequential lectin chromatography. On the other hand, elution from the lectin columns was followed by a clear increase in the affinity of the receptors as evidenced by (1) a decrease in the concentration of unlabeled insulin, causing half-maximal reduction of [125I]insulin binding, and (2) an increase in bound/free [125I]insulin (tracer binding) greater than the increase in binding capacity (saturation binding). This affinity shift was progressive on sequential lectin chromatography. Our findings indicate that the carbohydrate moiety of the insulin receptor contains N-acetylglucosamine, mannose, and galactose but that these saccharide residues are neither receptor nor tissue specific. The increase in affinity of the insulin receptor after its desorption from lectins may be due to separation from the binding site of an associated affinity regulator (inhibitor).

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