The carboxyl terminal segment of the c-Ki-ras 2 gene product mediates insulin-stimulated phosphorylation of calmodulin and stimulates insulin-independent autophosphorylation of the insulin receptor.
Cationic cofactors (e.g., polylysine or histone H2B) are necessary to observe phosphorylation of calmodulin in cell-free systems containing partially purified insulin receptors from a variety of tissues. The highly basic carboxyl terminus of the human c-Ki-ras 2 gene product stimulated both the in vitro phosphorylation of calmodulin and autophosphorylation of the beta-subunit of the insulin receptor, independently of insulin. Addition of insulin increased phosphate incorporation into calmodulin 2.5 fold. The K0.5 for insulin was approximately 5 x 10(-8) M. Maximal phosphorylation occurred at 120 microM c-Ki-ras 2 in the absence of Ca2+ and was inhibited by free Ca2+ concentrations above 0.1 microM. These data suggest the c-Ki-ras 2 gene product, an endogenous membrane protein, may play an important role in the cellular mechanism of insulin action.
Sacks
D B
DB
Washington University School of Medicine, St. Louis, Missouri 63110.
Glenn
K C
KC
McDonald
J M
JM
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002147:Calmodulin / Q000378:metabolism*; D066298:In Vitro Techniques; D007328:Insulin / Q000494:pharmacology*; D010446:Peptide Fragments / Q000494:pharmacology; D010766:Phosphorylation; D011107:Polylysine / Q000494:pharmacology; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D016283:Proto-Oncogene Proteins p21(ras); D051381:Rats; D011972:Receptor, Insulin / Q000378:metabolism*
D002147:Calmodulin; D007328:Insulin; D010446:Peptide Fragments; D011518:Proto-Oncogene Proteins; D011107:Polylysine; D011972:Receptor, Insulin; D016283:Proto-Oncogene Proteins p21(ras); D002118:Calcium