Binding of proinsulin and proinsulin conversion intermediates to human placental insulin-like growth factor I receptors.
Insulin-like growth factor I (IGF-I) and proinsulin share similarities in both primary and tertiary structure. Proinsulin, endogenously secreted or exogenously administered, would, therefore, be expected to interact with IGF-I receptors. We determined the relative activities of IGF-I, insulin, proinsulin, and the proinsulin conversion intermediates in IGF-I radioreceptor assays using term human placental membranes. Insulin was approximately 0.5% as potent as IGF-I, and proinsulin was only 2% as potent as insulin. The six major proinsulin conversion intermediates were studied; all had activities intermediate between those of insulin and proinsulin. We conclude that the binding of proinsulin and the proinsulin conversion intermediates to IGF-I receptors is not of physiological significance at the concentrations occurring endogenously or after exogenous administration of proinsulin.
Gruppuso
P A
PA
Division of Pediatric Metabolism, Rhode Island Hospital, Providence 02903.
Frank
B H
BH
Schwartz
R
R
D001667:Binding, Competitive; D005260:Female; D006801:Humans; D007328:Insulin / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy; D011384:Proinsulin / Q000378:metabolism*; D011485:Protein Binding; D011869:Radioligand Assay; D011972:Receptor, Insulin / Q000378:metabolism*; D017451:Receptors, Somatomedin; D011994:Recombinant Proteins / Q000378:metabolism; D013002:Somatomedins / Q000378:metabolism*
D007328:Insulin; D017451:Receptors, Somatomedin; D011994:Recombinant Proteins; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I; D011384:Proinsulin; D011972:Receptor, Insulin