Insulin rapidly stimulates phosphorylation of a 46-kDa membrane protein on tyrosine residues as well as phosphorylation of several soluble proteins in intact fat cells
It is speculated that the transmission of an insulin signal across the plasma membrane of cells occurs through activation of the tyrosine-specific receptor kinase, autophosphorylation of the receptor, and subsequent phosphorylation of unidentified substrates in the cell. In an attempt to identify possible substrates, the authors labeled intact rat fat cells with (/sup 32/P)orthophosphate and used an antiphosphotyrosine antibody to identify proteins that become phosphorylated on tyrosine residues in an insulin-stimulated way. In the membrane fraction of the fat cells, they found, in addition to the 95-kDa ..beta..-subunit of the receptor, a 46-kDa phosphoprotein that is phosphorylated exclusively on tyrosine residues. This protein is not immunoprecipitated by antibodies against different regions of the insulin receptor and its HPLC tryptic peptide map is different from the tryptic peptide map of the insulin receptor, suggesting that it is not derived from the receptor ..beta..-subunit. Insulin stimulates the tyrosine phosphorylation of the 46-kDa protein within 150 sec in the intact cell 3- to 4-fold in a dose-dependent way at insulin concentrations between 0.5 nM and 100 nM. Insulin (0.5 nM, 100 nM) stimulated within 2 min the /sup 32/P incorporation into a 116-kDa band, a 62 kDa band, and three bands between 45 kDa and 50 kDa 2- to 10-fold. They suggest that the 46-kDa membrane protein and possibly also the soluble proteins are endogenous substrates of the receptor tyrosine kinase in fat cells and that their phosphorylation is an early step in insulin signal transmission.
- Research Organization:
- Institut fuer Diabetesforschung, Munich, Germany, F.R.
- OSTI ID:
- 5520453
- Journal Information:
- Proc. Natl. Acad. Sci. U.S.A.; (United States), Vol. 84:1
- Country of Publication:
- United States
- Language:
- English
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ADIPOSE TISSUE
LABELLING
INSULIN
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PROTEINS
PHOSPHORYLATION
ANIMAL CELLS
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ENZYME INDUCTION
PHOSPHORUS 32
PHOSPHOTRANSFERASES
RATS
SWINE
TYROSINE
AMINO ACIDS
ANIMAL TISSUES
ANIMALS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
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DOMESTIC ANIMALS
ENZYMES
GENE REGULATION
HORMONES
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ORGANIC ACIDS
ORGANIC COMPOUNDS
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550201* - Biochemistry- Tracer Techniques