Extensive cAMP-dependent and cAMP-independent phosphorylation of microtubule-associated protein 2.
Microtubule-associated protein 2 (MAP 2) is the major substrate for phosphorylation in purified preparations of brain microtubules. In earlier work, we showed that phosphorylation is catalyzed by a type II cAMP-dependent protein kinase tightly associated with MAP 2 itself. In the present study, we have examined the extent of MAP 2 phosphorylation by its associated protein kinase. Using an inorganic phosphate assay, we found that MAP 2 contained from 8 to 13 mol of phosphate/mol of protein as isolated. The catalytic subunit of the MAP 2-associated kinase catalyzed the incorporation of additional phosphate to a final level of 20-22 mol/mol of MAP 2. Potato acid phosphatase was used to remove phosphate from MAP 2. Rephosphorylation of acid phosphatase-treated MAP 2 resulted in maximal incorporation of 13 mol of phosphate/mol of MAP 2. The rates and extent of [32P] phosphate incorporation into as isolated and dephosphorylated MAP 2 were found to be identical, and phosphate was incorporated into identical peptides in the two preparations. These results were interpreted to indicate that MAP 2 contains as many as 13 cAMP-dependent phosphorylation sites, and approximately eight phosphates of as yet undetermined origin.
D000818:Animals; D002417:Cattle; D002540:Cerebral Cortex / Q000201:enzymology*; D000242:Cyclic AMP / Q000494:pharmacology*; D007700:Kinetics; D008869:Microtubule-Associated Proteins; D008870:Microtubules / Q000378:metabolism*; D010446:Peptide Fragments / Q000032:analysis; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism*
D008869:Microtubule-Associated Proteins; D010446:Peptide Fragments; D011506:Proteins; D000242:Cyclic AMP; D011494:Protein Kinases