Phosphorylation activates the insulin receptor tyrosine protein kinase.
Preparations of insulin receptor from cultured 3T3-L1 adipocytes and human placenta previously was found to catalyze the phosphorylation of the 90,000-dalton component of the insulin receptor on tyrosine residues. This insulin-dependent phosphorylation has now been shown to coincide with the generation of an activated, insulin-independent, receptor protein kinase. Activation is dependent upon ATP, divalent cations (Mg2+ and Mn2+), and insulin (half-maximal activation occurs at 6-8 nM insulin). The time required for activation is consistent with that needed for insulin-dependent self-phosphorylation of the receptor present in eluates from wheat germ lectin-agarose columns and in preparations of affinity-purified placental receptor. Activation proceeds unabated in the presence of soybean trypsin inhibitor at 0.1 mg/ml and the activated, insulin-independent, protein kinase sediments in 5-20% sucrose gradients at the same position as the unmodified receptor. Under steady-state conditions, the phosphorylated receptor binds insulin in the same fashion as the unmodified receptor. It is proposed that the self-phosphorylated form of the receptor is the insulin-activated protein kinase that catalyzes the phosphorylation of exogenous protein and peptide substrates. A corollary of this hypothesis is that enzymatic dephosphorylation may be essential for reversibly terminating the activity of the insulin-receptor protein kinase.
D000255:Adenosine Triphosphate / Q000378:metabolism; D000273:Adipose Tissue / Q000378:metabolism; D000818:Animals; D002413:Cations, Divalent; D002454:Cell Differentiation; D002478:Cells, Cultured; D004789:Enzyme Activation; D005260:Female; D006801:Humans; D007700:Kinetics; D051379:Mice; D010766:Phosphorylation; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy; D011494:Protein Kinases / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases; D011972:Receptor, Insulin / Q000378:metabolism*
D002413:Cations, Divalent; D000255:Adenosine Triphosphate; D011494:Protein Kinases; D011505:Protein-Tyrosine Kinases; D011972:Receptor, Insulin