Calcium/calmodulin-dependent protein kinase belonging to a proposed calcium-triggered signaling cascade. In vitro, isoform 1 and isoform 2 phosphorylate CREB1, SYN1/synapsin I. Phosphorylates and activates CAMK1. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Activated by Ca(2+)/calmodulin. Must be phosphorylated to be maximally active. Activated by CAMKK1. Isoform 1 is expressed in liver, heart, lung, kidney, spleen and testis. Isoform 2 is predominantly expressed in cerebrum and cerebellum. Isoform 1 and isoform 2 are phosphorylated by CAMKK1. Belongs to the protein kinase superfamily. CAMK Ser/Thr protein kinase family. CaMK subfamily.