Calmodulin-dependent kinase that phosphorylates MYL2 in vitro. Promotes sarcomere formation in cardiomyocytes. Increases cardiomyocyte contractility. ATP + L-seryl-[myosin light chain] = ADP + H(+) + O-phospho-L-seryl-[myosin light chain] ATP + L-threonyl-[myosin light chain] = ADP + H(+) + O-phospho-L-threonyl-[myosin light chain] Expressed in cardiomyocytes (at protein level). Up-regulated in heart after experimental myocardial infarction at the mRNA level. Up-regulated in the heart from 1 week after birth through adulthood. by NRG1 (at protein level). Phosphorylated on serine residues. Belongs to the protein kinase superfamily. CAMK Ser/Thr protein kinase family.