CYTOSKELETAL-ASSOCIATED PROTEIN-KINASE AND PHOSPHATASE-ACTIVITIES FROM CEREBRAL-CORTEX OF YOUNG-RATS

We describe the phosphorylation system associated with the Triton-insoluble cytoskeletal fraction that phosphorylates in vitro the 150 kDa neurofilament subunit (NF-M) and alpha and beta tubulin from cerebral cortex of rats. The protein kinase activities were determined in the presence of 20 mu M cyclic AMP (cAMP), 1 mM calcium and 1 mu M calmodulin (Ca2+/calmodulin) or 1 mM calcium, 0.2 mM phosphatidylserine and 0.5 mu M phorbol 12,13-dibutyrate (Ca2+/PS/PDBu). Phosphorylation of these cytoskeletal proteins increased approximately 35% and 65% in the presence of cAMP and Ca2+/calmodulin, respectively, but was unaffected in the presence of Ca2+/PS/PDBu. Basal phosphorylation of these proteins studied increased approximately 35% and 72% in the presence of 0.5 mu M okadaic acid and 0.01 mu M microcystin-LR, respectively, suggesting the presence of phosphatase type 1. Results suggest that at least two protein kinases and one protein phosphatase are associated with the Triton-insoluble cytoskeletal fraction from cerebral cortex of rats.