The insulin-like growth factor II receptor is phosphorylated by a tyrosine kinase in adipocyte plasma membranes.
Incorporation of 32P from [gamma-32P]ATP into tyrosine residues of the insulin-like growth factor (IGF)-II receptor was observed in a Triton X-100-insoluble fraction of rat adipocyte plasma membranes. IGF-II receptor phosphorylation proceeded to a stoichiometry of approximately 0.5 mol of phosphate/IGF-II binding site after 10 min of incubation at 4 degrees C. A Km for ATP of 6 microM was calculated for this phosphorylation reaction. Addition of IGF-II caused an approximately 2-fold increase in tyrosine phosphorylation of the IGF-II receptor in this preparation. In contrast, phosphorylation of angiotensin II by the Triton X-100 washed membranes was not stimulated by IGF-II. Incubation of purified receptor immobilized on IGF-II agarose or of receptor-enriched low density microsomal membranes with [gamma-32P]ATP did not result in appreciable incorporation of [32P]phosphate into the IGF-II receptor nor into exogenous substrates. These data suggest that the IGF-II receptor is not a tyrosine protein kinase capable of autophosphorylation but that it is a substrate for a tyrosine protein kinase endogenous to the adipocyte plasma membrane. The stimulatory effect of IGF-II on the tyrosine phosphorylation of its receptor may be due to a conformational change which converts the receptor to a better substrate for this tyrosine kinase.
Corvera
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S
Whitehead
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Mottola
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C
Czech
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MP
D000255:Adenosine Triphosphate / Q000378:metabolism; D000273:Adipose Tissue / Q000201:enzymology / Q000378:metabolism*; D000804:Angiotensin II / Q000378:metabolism; D000818:Animals; D002462:Cell Membrane / Q000201:enzymology; D007335:Insulin-Like Growth Factor II / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D008970:Molecular Weight; D010761:Phosphorus Radioisotopes; D019000:Phosphotyrosine; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D011956:Receptors, Cell Surface / Q000302:isolation & purification / Q000378:metabolism*; D017451:Receptors, Somatomedin; D013002:Somatomedins / Q000378:metabolism*; D014443:Tyrosine / Q000031:analogs & derivatives / Q000032:analysis
D010761:Phosphorus Radioisotopes; D011956:Receptors, Cell Surface; D017451:Receptors, Somatomedin; D013002:Somatomedins; D000804:Angiotensin II; D019000:Phosphotyrosine; D014443:Tyrosine; D007335:Insulin-Like Growth Factor II; D000255:Adenosine Triphosphate; D011505:Protein-Tyrosine Kinases