Calcium/calmodulin-dependent protein kinase belonging to a proposed calcium-triggered signaling cascade involved in a number of cellular processes. Isoform 1, isoform 2 and isoform 3 phosphorylate CAMK1 and CAMK4. Isoform 3 phosphorylates CAMK1D. Isoform 4, isoform 5 and isoform 6 lacking part of the calmodulin-binding domain are inactive. Efficiently phosphorylates 5'-AMP-activated protein kinase (AMPK) trimer, including that consisting of PRKAA1, PRKAB1 and PRKAG1. This phosphorylation is stimulated in response to Ca2+ signals By similarity. Seems to be involved in hippocampal activation of CREB1 By similarity. May play a role in neurite growth. Isoform 3 may promote neurite elongation, while isoform 1 may promoter neurite branching.Hsu L.-S., J. Biol. Chem. 276:31113-31123(2001).Anderson K.A., J. Biol. Chem. 273:31880-31889(1998).Ishikawa Y., FEBS Lett. 550:57-63(2003).