CA2-MEDIATED PHOSPHORYLATION AND PROTEOLYSIS ACTIVITY ASSOCIATED WITHTHE CYTOSKELETAL FRACTION FROM CEREBRAL-CORTEX OF RATS()

We describe a Triton-insoluble cytoskeletal fraction extracted from ce rebral cortex of young rats retaining an endogenous Ca2+-mediated mech anism acting in vitro on Ca2+/calmodulin-dependent protein kinase II ( CaM-KII) activity and on phosphorylation and proteolysis of the 150 kD a neurofilament subunit (NF-M), alpha and beta tubulin. Exogenous Ca2 induced a 70% decrease in the in vitro phosphorylation of the NF-M an d tubulins and a 30-50% decrease in the total amount of these proteins . However, when calpastatin was added basal phosphorylation and NF-M a nd tubulin content were recovered. Furthermore, exogenous Ca2+/calmodu lin induced increased in vitro phosphorylation of the cytoskeletal pro teins and CaM-KII activity only in the presence of calpastatin, sugges ting the presence of Ca2+-induced calpain-mediated proteolysis. This f raction could be an interesting model to further studies concerning th e in vitro effects of Ca2+-mediated protein kinases and proteases asso ciated with the cytoskeletal fraction.