The subunit structure of the high affinity insulin receptor. Evidence for a disulfide-linked receptor complex in fat cell and liver plasma membranes.

摘要: 125I-Insulin equilibrated with high affinity fat cell and liver plasma membrane receptors was cross-linked to the by addition of disuccinimidyl suberate. Autoradiographic analysis 125I-insulin-linked membranes subsequent dodecyl sulfate electrophoresis in absence reductant revealed presence one labeled species which migrated an apparent molecular weight 300,000. Electrophoresis these dithiothreitol resulted appearance major band about Mr = 125,000 concomitant loss label 300,000 region. Another radioactive 225,000 region on reduced gels contained a much smaller amount label. The degree component 125I-insulin experiments paralleled extent occupancy 125I-insulin. 125I-Insulin-linked derived from adipocytes alkylated N-ethylmaleimide prior homogenization prevent spontaneous sulfhydryl oxidation also exhibited bands upon reductant, respectively. These same were observed when covalently corss-linked intact adipocytes. data indicate that monomer 125,00 represents insulin receptor subunit exists native adipocyte disulfide-linked complex. present form (Mr 125,000) only 20 30% oxidized 300,000). Since used studies is predominantly A chain, this large reduction indicates it B chain linked protein 125I-Proinsulin lacks NH2 terminus could be receptor, indicating A1 glycine not critical cross-linking reaction. 125I-Insulins modified either at lysine B29 acetyl group or phenylalanine B1 phenylthiocarbamoyl both readily roughly equal efficiency. It concluded terminal amino groups are accessible for