Ischemic brain injury selectively alters ATP binding of calcium and calmodulin-dependent protein kinase II

Calmodulin and ATP affinity and total binding capacity were characterized for CaM kinase II isolated from control and ischemic animals. Ischemic CaM kinase II exhibited equivalent apparent affinity and total binding for calmodulin when compared to control enzyme. However, ischemic CaM kinase II exhibited a significant decrease in apparent affinity for ATP in saturation experiments. ATP binding was characterized using the ATP photoaffinity analog [alpha-32P] Azido-ATP. A significant decrease in total binding and binding affinity for ATP was observed for the alpha (50 kDa) and beta (60 kDa) subunits. The observation that ischemia induced an alteration of ATP binding without affecting calmodulin binding is consistent with the hypothesis that ischemia directly affects the ATP binding of CaM kinase II which results in subsequent inhibition of the enzyme.