| Abstract: | Treatment of membrane vesicles from A431 cells, a human epidermoid carcinoma line, with the affinity label 5'-p-fluorosulfonylbenzoyl [8-14C]adenosine (5'-p-FSO2Bz[14C]Ado) results in an inhibition of the epidermal growth factor (EGF)-stimulable protein kinase and in the modification of proteins having the same molecular weight (Mr = 170,000 and 150,000) as the receptor for EGF (Buhrow, S. A., Cohen, S., and Staros, J. V. (1982) J. Biol. Chem. 257, 4019-4022). Modification of the vesicles with 5'-p-FSO2BzAdo inhibits not only the EGF-stimulated phosphorylation of endogenous membrane proteins but also the EGF-stimulated phosphorylation of an exogenous synthetic tyrosine-containing peptide substrate. This indicates that the EGF-stimulable protein kinase is modified by 5'-p-FSO2BzAdo at a site affecting catalytic activity. Membrane vesicles were treated with 5'-p-FSO2Bz-[14C]Ado to affinity label the kinase, then the EGF receptor was purified by affinity chromatography on immobilized EGF. The EGF receptor thus purified contains the 5'-p-SO2Bz[14C]Ado moiety. These data strongly support our hypothesis that the EGF receptor and EGF-stimulable kinase are two parts of the same polypeptide chain. |
