PHOSPHORYLATION BY MAPKAP KINASE-2 ACTIVATES MG2-ATPASE ACTIVITY OF MYOSIN-II()

Mitogen-activated protein kinase activated protein (MAPKAP) kinase-2 w as found to phosphorylate the regulatory light chain of myosin II (MRL C) in vitro in the absence of Ca2+/calmodulin. The tryptic peptides re covered 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 w as phosphorylated by the kinases at the serine residue. This phosphory lation by MAPKAP kinase-2 activated the actin-activated Mg2+-ATPase ac tivity of myosin II. These findings indicated that MAPKAP kinase-2 may be a kinase that regulates the actin-activated Mg2+-ATPase activity o f myosin II. (C) 1996 Academic Press, Inc.