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Rapid Stimulation by Insulin of a Serine/Threonine Kinase in 3T3-L1 Adipocytes that Phosphorylates Microtubule-Associated Protein 2 in vitro

L. Bryan Ray and Thomas W. Sturgill
Proceedings of the National Academy of Sciences of the United States of America
Vol. 84, No. 6 (Mar. 15, 1987), pp. 1502-1506
Stable URL: http://www.jstor.org/stable/29610
Page Count: 5
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Rapid Stimulation by Insulin of a Serine/Threonine Kinase in 3T3-L1 Adipocytes that Phosphorylates Microtubule-Associated Protein 2 in vitro
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Abstract

Insulin treatment (Kact, 5 × 10-9 M) of serum-starved 3T3-L1 adipocytes stimulates a soluble serine/threonine kinase that catalyzes phosphorylation of microtubule-associated protein 2 (MAP-2) in vitro. Maximal activation of MAP-2 kinase activity by 80 nM insulin was observed after 10 min of hormonal stimulation, prior to maximal stimulation of S6 kinase activity (20 min). The insulin-stimulatable MAP-2 kinase activity is not adsorbed to phosphocellulose, whereas the principal S6 kinase activity is retained and elutes at ≈ 0.5 M NaCl. The insulin-stimulatable MAP-2 kinase is less stable during incubation at 30 degrees C than S6 kinase activity. Inclusion of phosphatase inhibitors decreases the rate at which the stimulated MAP-2 kinase activity is lost from extract supernatants incubated at 30 degrees C. p-Nitrophenyl phosphate is more effective than DL-phosphotyrosine, whereas DL-phosphoserine is without effect at the concentration used (40 mM). The difference in MAP-2 kinase activity in extract supernatants from control and insulin-treated cells is also preserved after rapid chromatography on Sephadex G-25. These results show that a soluble serine/threonine kinase is rapidly activated by insulin, possibly by phosphorylation of either the kinase itself or an interacting modulator.

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