J. Biol. Chem., Vol. 261, Issue 17, 7675-7679, Jun, 1986
The insulin-like growth factor II receptor is phosphorylated by a tyrosine kinase in adipocyte plasma membranes
S Corvera, RE Whitehead, C Mottola and MP Czech
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.