The human placenta contains two distinct binding and immunoreactive species of insulin-like growth factor-I receptors.
Two species of insulin-like growth factor-I (IGF-I) receptors in human placenta have been delineated on the basis of their immunoreactivity with an autoantiserum (B-2) to the insulin receptor. When all the IGF-I binding sites in solubilized human placenta were assayed by polyethylene glycol precipitation, a curvilinear Scatchard plot was obtained which could be resolved into two single classes of binding sites: one immunoprecipitable by B-2 IgG and the other, nonimmunoprecipitable. The B-2 reactive sites bound IGF-I with lower affinity (Kd = 7.1 X 10(-10) M) than the B-2 nonreactive sites (Kd = 2.1 X 10(-10) M) and cross-reacted more readily with insulin, the IGF-I/insulin-binding potencies being congruent to 120 and congruent to 1100, respectively. Both receptor subtypes bound IGF-I with congruent to 30-fold higher affinity than multiplication-stimulating activity, and, after affinity cross-linking with 125I-IGF-I, migrated as specific reduced bands of Mr = 138,000 during sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The subunit sizes of the B-2 reactive IGF-I receptor were similar to those of the insulin receptor. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of 125I-labeled receptors immunoprecipitated by autoantiserum B-2 or autoantiserum B-10 (which recognizes only insulin receptors) revealed, in both cases, specific reduced bands of Mr = 130,000 and 90,000; the same bands were also seen after sequential precipitation with B-10 and B-2 antisera to enrich the proportion of IGF-I receptors recovered. The presence of two distinct binding and immunoreactive species of IGF-I receptors in human placenta raises the possibility that cell- or tissue-specific isotypes of the IGF-I receptor could mediate the different biological actions of IGF-I.
Jonas
H A
HA
Harrison
L C
LC
D011232:Chemical Precipitation; D000939:Epitopes / Q000276:immunology; D005260:Female; D006801:Humans; D007106:Immune Sera / Q000276:immunology; D007074:Immunoglobulin G / Q000276:immunology; D007163:Immunosorbent Techniques; D007328:Insulin / Q000378:metabolism; D008970:Molecular Weight; D010455:Peptides / Q000378:metabolism; D010920:Placenta / Q000378:metabolism*; D011092:Polyethylene Glycols; D011247:Pregnancy; D011956:Receptors, Cell Surface / Q000276:immunology / Q000378:metabolism*; D017451:Receptors, Somatomedin; D013002:Somatomedins / Q000378:metabolism
D000939:Epitopes; D007106:Immune Sera; D007074:Immunoglobulin G; D007328:Insulin; D010455:Peptides; D011956:Receptors, Cell Surface; D017451:Receptors, Somatomedin; D013002:Somatomedins; D011092:Polyethylene Glycols