Serine/threonine protein kinases frequently bind to CaM, autophosphorylate, and phosphorylate substrates in a Ca(2+)/CaM-dependent manner. In this way, the serine protein kinase activity is activated after the EF-Hand of F13 binds to Ca2+ and then binds Mg2+-ATP. Once PK Tyr Ser-Thr was autophosphorylated and phosphoinositide was phosphorylated, F13's serine protein kinase activity was lost. Rebinding of F13 to Mg2+-ATP should activate its Serine phosphatase (PPM) domain. Since PK_Tyr_Ser-Thr shares similarities sites with Dynamin-type B, it is likely that they both play important roles in the body. The dephosphorylation of the PK Tyr Ser-Thr domain by the PPM domain directly causes the binding of Mg2+-GTP to Asn132 and the activation of Dynamin GTPase activity.