Autophosphorylation of Calmodulin-Dependent Protein Kinase IV from Rat Cerebral Cortex

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Calmodulin-dependent protein kinase IV from rat cerebral cortex undergoes autophosphorylation in response to Ca²⁺ and calmodulin, resulting in its marked enzymatic activation. Autophosphorylation occurred at several sites on CaM-kinase IV, depending upon the enzyme concentration. Among them, Ser⁴³⁷ was almost exclusively phosphorylated at enzyme concentrations lower than 10 μg/ml, and autophosphorylation at Ser⁴³⁷ was responsible for marked activation of the enzyme through decreases in the K_m values for its substrates and an increase in the V_max value. The Ca²⁺/calmodulin-independent activity of CaM-kinase IV was also markedly stimulated by autophosphorylation, but even after autophosphorylation it amounted only about 17% of the total enzyme activity detected in the presence of Ca²⁺/calmodulin.