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pubmed:abstractText |
Platelet-derived growth factor (PDGF) stimulates the incorporation of 32P from [gamma-32P]ATP into a Mr approximately 170,000 protein by an endogenous tyrosine-specific protein kinase in membrane preparations of Swiss mouse 3T3 cells. Epidermal growth factor (EGF), but not fibroblast growth factor (FGF) or insulin, stimulates limited incorporation of 32P into a protein of similar molecular weight. The ligand concentration required for half-maximal activity (S0.5) for PDGF stimulation of phosphorylation is 50 ng/ml; saturation is achieved at 300 ng/ml. The S0.5 for ATP is 15 microM. Mg2+ or Mn2+ is required for protein kinase activity. Stimulation of PDGF results in the preferential phosphorylation of tyrosine residues in this Mr approximately 170,000 membrane protein. The Mr approximately 170,000 protein can be resolved into Mr approximately 180,000 and 160,000 components in 4% NaDodSO4 gels. PDGF stimulates 32P incorporation preferentially into the Mr approximately 180,000 and less extensively into the Mr approximately 160,000 protein. EGF stimulates 32P incorporation predominantly into a protein of Mr approximately 160,000. The similarity of PDGF and EGF in stimulating phosphotyrosine-specific protein kinase activity and the stimulation of a similar activity by viral transformation (src) genes suggest that a common mechanism may exist for the phenotypic expression of increased DNA synthesis and cell growth stimulated by these separate factors.
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