Phosphorylation by MAPKAP kinase 2 activates Mg(2+)-ATPase activity of myosin II

Mitogen-activated protein kinase activated protein (MAPKAP) kinase-2 was found to phosphorylate the regulatory light chain of myosin II (MRLC) in vitro in the absence of Ca2+/calmodulin. The tryptic peptides recovered from the MRLC phosphorylated by MAPKAP kinase-2 were identical to the phosphopeptides recovered from myosin light chain kinase (MLCK)-phosphorylated MRLC. Phosphoamino acid analysis revealed that MRLC was phosphorylated by these kinases at the serine residue. This phosphorylation by MAPKAP kinase-2 activated the actin-activated Mg(2+)-ATPase activity of myosin II. These findings indicated that MAPKAP kinase-2 may be a kinase that regulates the actin-activated Mg(2+)-ATPase activity of myosin II.