Abstract
The purified insulin receptor kinase catalyzed the phosphorylation of native tubulin and microtubule-associated proteins (MAPs; MAP2, tau) on tyrosine residues. Insulin (10(-7) M) stimulated the reaction by 4-10-fold by increasing Vmax with little change in Km. alpha-Tubulin was preferred as a substrate for the kinase compared to beta-tubulin. MAP2 was found to be the best substrate among the cytoskeletal proteins tested; in the presence of insulin, the Vmax for MAP2 was 6.3 nmol/min/mg, its Km was 5.1 microM, and 1.7 mol of phosphate were incorporated per mol of MAP2. Under the same conditions used for this phosphorylation of tubulin and MAPs, actin and tropomyosin were very poorly phosphorylated. These data, coupled with previous evidence for potential functional relationships between insulin action and microtubules, raise the possibility that microtubule proteins may be cellular targets for the insulin receptor kinase.
Highlights
The purified .insulin receptor kinase catalyzed the insulin receptor kinase because they are ubiquitous proteins phosphorylation of native tubulinandmicrotubule- in all eukaryotic cells, are located close to the plasma memassociatedproteins (MAPs;MAPB,tau) residues
We report that purified insulin receptor kinase can phosphorylate native tubulin, the major protein of microtubules, and microtubule-associated proteins (MAPS') in a cell
The following materials were obtained from the sources indicated; gene responsible for transformation by Rous sarcoma virus), [r-'*P]ATP was from New England Nuclear; reagents for sodium and angiotensin I1 have been shown to be phosphorylated by the purified insulin receptor kinase [10, 11].these substratescannot bephysiologically relevant cellular substrates because of their localization and nature
Summary
The purified .insulin receptor kinase catalyzed the insulin receptor kinase because they are ubiquitous proteins phosphorylation of native tubulinandmicrotubule- in all eukaryotic cells, are located close to the plasma memassociatedproteins (MAPs;MAPB,tau) residues. 401&4020,1985 Printed in U.S.A. Phosphorylation of Tubulin and Microtubule-associatedProteins by the Purified Insulin Receptor Kinase* We report that purified insulin receptor kinase can phosphorylate native tubulin, the major protein of microtubules, and microtubule-associated proteins (MAPS') in a cell
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