Insulin stimulates a membrane-bound serine kinase that may be phosphorylated on tyrosine.
Triton X-100-solubilized high-density microsomes from insulin-treated rat adipocytes exhibit a marked increase in serine/threonine and tyrosine kinase activities toward exogenous histone when compared to controls. The insulin-dependent activation of microsomal histone kinase activities occurs within the physiological range of hormone concentrations (ED50 = 0.6 nM). The hormone-enhanced histone phosphorylation by the high-density microsomes appears to be catalyzed by two distinct kinases, based on their differential interaction with wheat germ agglutinin-agarose. The insulin-sensitive serine/threonine kinase is not retained by The insulin-sensitive serine/threonine kinase is not retained by the lectin column, whereas the tyrosine kinase appears to be a glycoprotein as evidenced by its adsorption to the immobilized lectin. The insulin-stimulated serine/threonine kinase exhibits preferential phosphorylation of histone and Kemptide (synthetic Leu-Arg-Arg-Ala-Ser-Leu-Gly) compared to a number of other peptide substrates. The substrate specificity of this serine/threonine kinase shows that it is distinct from the kinases that phosphorylate ribosomal protein S6, casein, phosvitin, ATP citrate lyase, and glycogen synthase and from multifunctional calmodulin-dependent, cAMP- and cGMP-dependent, and Ca2+/phospholipid-dependent protein kinases. Furthermore, 22% of the insulin-sensitive serine/threonine kinase activity can be adsorbed by monoclonal anti-phosphotyrosine antibodies immobilized on agarose. Its adsorption is specifically inhibited by excess free phosphotyrosine but not phosphoserine or phosphothreonine. The data suggest that this insulin-stimulated serine/threonine kinase in adipocyte high-density microsomes is tyrosine-phosphorylated, consistent with the hypothesis that the stimulatory action of insulin on this kinase may be mediated by tyrosine phosphorylation.
D000273:Adipose Tissue / Q000201:enzymology*; D000818:Animals; D000906:Antibodies; D000936:Antigen-Antibody Complex / Q000032:analysis; D007328:Insulin / Q000494:pharmacology*; D007700:Kinetics; D008297:Male; D008861:Microsomes / Q000201:enzymology*; D010766:Phosphorylation; D019000:Phosphotyrosine; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D051381:Rats; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000032:analysis
D000906:Antibodies; D000936:Antigen-Antibody Complex; D007328:Insulin; D019000:Phosphotyrosine; D014443:Tyrosine; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases