Abstract: | Ca2+-calmodulin tubulin kinase activity was isolated from brain cytosol and separated from its substrate protein, tubulin, and Ca2+ regulatory protein, calmodulin. Characterization of the Ca2+-tubulin kinase system revealed a Km of 4 μM, 0.5 μM, 60 μM for Ca2+, calmodulin and ATP, respectively. The tubulin kinase system bound to a calmodulin affinity column in the presence of Ca2+ and was released from the column by chelation with EGTA. A major 55,000 and a minor 65,000 dalton peptide were identified as the only calmodulin binding proteins in the enzyme fraction, indicating that one or both of these peptides represent the calmodulin binding subunit of the Ca2+-calmodulin tubulin kinase system. |