The action of PKA on smooth muscle myosin phosphorylation

The aim of the study is to reveal the characterization of PKA acting on myosin. We found: (a) in the absence of Ca2+/CaM, PKA slightly phosphorylated MLC20 and stimulated the Mg2+-ATPase activity of myosin, which was strengthened significantly by arachidonic acid (ACAD); (b) Ca2+-independent phosphorylation of myosin by PKA was obviously less efficient than both Ca2+-dependent and independent phosphorylation of myosin by MLCK; (c) micro-amount of calponin could not increase the precipitation of myosin phosphorylated by PKA, but it increased the precipitation of myosin phosphorylated by MLCK, suggesting the presence of conformational differences between the myosins phosphorylated by PKA and by MLCK.