Functional properties of an isolated alpha beta heterodimeric human placenta insulin-like growth factor 1 receptor complex.
Treatment of human placenta membranes at pH 8.5 in the presence of 2.0 mM dithiothreitol (DTT) for 5 min, followed by the simultaneous removal of the DTT and pH adjustment to pH 7.6, resulted in the formation of a functional alpha beta heterodimeric insulin-like growth factor 1 (IGF-1) receptor complex from the native alpha 2 beta 2 heterotetrameric disulfide-linked state. The membrane-bound alpha beta heterodimeric complex displayed similar curvilinear 125I-IGF-1 equilibrium binding compared to the alpha 2 beta 2 heterotetrameric complex. Triton X-100 solubilization of the alkaline pH and DTT-pretreated placenta membranes, followed by Bio-Gel A-1.5m gel filtration chromatography, was found to effectively separate the alpha 2 beta 2 heterotetrameric and alpha beta heterodimeric IGF-1 receptor species, 125I-IGF-1 binding to both the isolated alpha 2 beta 2 heterotetrameric and alpha beta heterodimeric complexes demonstrated a marked straightening of the Scatchard plots, compared to the placenta membrane-bound IGF-1 receptors, with a 2-fold increase in the high-affinity binding component. Similar to the membrane-bound IGF-1 receptor species, the 125I-IGF-1 binding properties between the alpha 2 beta 2 heterotetrameric and alpha beta heterodimeric complexes were not significantly different. IGF-1 stimulation of IGF-1 receptor autophosphorylation indicated that the ligand-dependent activation of alpha beta heterodimeric protein kinase activity occurred concomitant with the reassociation into a covalent alpha 2 beta 2 heterotetrameric state.(ABSTRACT TRUNCATED AT 250 WORDS)
Feltz
S M
SM
Department of Physiology and Biophysics, University of Iowa, Iowa City 52242.
Swanson
M L
ML
Wemmie
J A
JA
Pessin
J E
JE
D001667:Binding, Competitive; D002462:Cell Membrane / Q000378:metabolism; D002850:Chromatography, Gel; D005260:Female; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D007700:Kinetics; D046911:Macromolecular Substances; D008970:Molecular Weight; D010766:Phosphorylation; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy; D011972:Receptor, Insulin / Q000302:isolation & purification / Q000378:metabolism*; D017451:Receptors, Somatomedin; D013002:Somatomedins / Q000378:metabolism*
D046911:Macromolecular Substances; D017451:Receptors, Somatomedin; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I; D011972:Receptor, Insulin