Ca~(2+)-independent Phosphorylation of Myosin on Smooth Muscle Myosin by Myosin Light Chain Kinase

The characterization of Ca~(2+)-independent phosphorylation of myosin by MLCK was investigated.The results indicated that MLCK phosphorylated myosin not only in the Ca~(2+)-dependent way,but also in a Ca~(2+)-independent way.By using MLCK,the Ca~(2+)-independent phosphorylation of myosin needed much higher concentration of MLCK,and was less influenced by increasing the incubation temperature,prolonging incubation time,and increasing the K~+-ion strength compared to the Ca~(2+)-dependcnt phosphorylation.The results suggest that the Ca~(2+)-independent phosphorylation of myosin by MLCK be a new mechanism and involve in maintaining the tension of smooth muscle.