Solubilization and partial purification of protein kinase systems from brain membranes that phosphorylate calspectin

In brain tissue a spectrin-like calmodulin-binding protein calspectin, or fodrin, is concentrated in a synaptosome fraction, where most of the calspectin is associated with the synaptic membranes. This endogenous calspectin was phosphorylated by protein kinase system(s) associated with the membranes. Here, we report the solubilization and partial purification of the membrane-associated calspectin kinase activity. The activity was resolved on a gel filtration column into two fractions, peaks I and II having estimated Mrof 800 000 and 88 000. The activity of peak I was dependent on the presence of both Ca 2+and calmodulin. Peak II revealed a basal activity in the absence of Ca 2+and calmodulin, which was stimulated 2-fold by addition of Ca 2+. Calmodulin had no effect on the peak II activity.