Characterization of insulin-like growth factor I-stimulated tyrosine kinase activity associated with the beta-subunit of type I insulin-like growth factor receptors of rat liver cells.

摘要: We previously reported that insulin-like growth factor I (IGF-I) stimulates the phosphorylation of a Mr 98,000 protein thought to be beta-subunit type IGF receptor BRL-3A2 rat liver cells, as well exogenous tyrosine-containing substrate poly(Glu,Tyr), 4:1. The present study provides additional evidence possesses intrinsic tyrosine kinase activity and characterizes properties this kinase. IGF-I 4:1, by lectin-purified preparations with same concentration dependence; half-maximal stimulation was observed approximately 3 nM 3-fold higher concentrations insulin. Although IGF-I-dependent within 2 min maximal after 10 min, did not begin increase until 8 addition [gamma-32P] ATP When IGF-I-receptor complexes were preincubated unlabeled for before substrate, however, 32P incorporation increased linearly 20 min. propose activation results from autophosphorylation Kinase is an intramolecular reaction, specific ATP, occurs requires presence or concomitant ATP. acts rapidly, stimulating I-IGF closely resemble those insulin kinase, suggesting homologies between two receptors extend their domains.