Calmodulin-dependent protein kinase (kinase II) which is involved in the activation of tryptophan 5-monooxygenase catalyzes phosphorylation of tubulin.

Tubulin was shown to be an endogenous substrate of the calmodulin-dependent protein kinase (kinase II), which is involved in the activation of tryptophan 5-monooxygenase [T. Yamauchi and H. Fujisawa (1983) Eur. J. Biochem. 132, 15-21]. Serine and threonine were identified as the phosphate acceptor amino acids of tubulin. The Vmax of the phosphorylation of tubulin and the apparent Km value for tubulin of calmodulin-dependent protein kinase II were 89 nmol phosphate transferred min-1 mg kinase II-1 and 1.7 microM, respectively. The maximum 32P incorporation into tubulin was 0.18 mol Pi/mol alpha-tubulin and 0.13 mol Pi/mol beta-tubulin. The phosphorylation of tubulin was decreased by the denaturation of tubulin. The phosphorylation of tubulin by kinase II did not affect the assembly of microtubules.