title: Fluorescence correlation spectroscopic examination of insulin and insulin-like growth factor 1 binding to live cells.
abstract: We used fluorescence correlation spectroscopy to examine the binding of insulin, insulin-like growth factor 1 (IGF1) and anti-receptor antibodies to insulin receptors (IR) and IGF1 receptors (IGF1R) on individual 2H3 rat basophilic leukemia cells. Experiments revealed two distinct classes of insulin binding sites with K(D) of 0.11 nM and 75 nM, respectively. IGF1 competes with insulin for a portion of the low-affinity insulin binding sites with K(D) of 0.14 nM and for the high-affinity insulin binding sites with K(D) of 10 nM. Dissociation rate constants of insulin and IGF1 were determined to be 0.015 min(-1) and 0.013 min(-1), respectively, allowing estimation of ligand association rate constants. Combined, our results suggest that, in addition to IR and IGF1R homodimers, substantial numbers of hybrid IR-IGF1R heterodimers are present on the surface of these cells.
authors.affiliation: Cell and Molecular Biology Program, Colorado State University, Fort Collins, Colorado 80523, USA.
authors.forename: Peter W
authors.initials: PW
authors.lastname: Winter
authors.forename: Jeffrey T
authors.initials: JT
authors.lastname: McPhee
authors.forename: Alan K
authors.initials: AK
authors.lastname: Van Orden
authors.forename: Deborah A
authors.initials: DA
authors.lastname: Roess
authors.forename: B George
authors.initials: BG
authors.lastname: Barisas
mesh_terms: D000818:Animals; D000906:Antibodies / Q000276:immunology; D001665:Binding Sites; D045744:Cell Line, Tumor; D007328:Insulin / Q000737:chemistry / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D051381:Rats; D017526:Receptor, IGF Type 1 / Q000276:immunology / Q000378:metabolism*; D011972:Receptor, Insulin / Q000276:immunology / Q000378:metabolism*; D013050:Spectrometry, Fluorescence
chemical_list: D000906:Antibodies; D007328:Insulin; D007334:Insulin-Like Growth Factor I; D017526:Receptor, IGF Type 1; D011972:Receptor, Insulin