Phosphorylation of Ca2+/Calmodulin-Dependent Protein Kinase V and Regulation of Its Activity

Autophosphorylation of Ca2+/calmodulin-dependent protein kinase V (CaM kinaseV) resulted in a drastic potentiation of the Ca2+/calmodulin-dependent activity, but Ca2+/calmodulin-independent activity was not generated. The rate of autophosphorylation increased with increases in the enzyme concentration, thereby suggesting intermolecular reactions. In the course of these investigations, another factor by which CaM kinase V is also phosphorylated and activated became evident. The addition of EGTA blocked CaM kinase V phosphorylation. The autophosphorylated CaM kinase V was not phosphorylated by the activator. These observations suggest that the activation factor is a CaM kinase which phosphorylates CaM kinase V at the autophosphorylation site, thereby potentiating the enzymatic activity.