Contraction myosin regulatory light chain

In smooth muscle, contraction is controlled by the phosphorylation state of the myosin regulatory light chain. The extent of this phosphorylation will depend on the regulatory states of both myosin light chain kinase (MLCK) and of... 

Contraction of smooth muscle and nonmuscle cells Is triggered by phosphorylation of the myosin regulatory light chains either by myosin LC kinase. In response to a rise In cytosolic Ca ", or by Rho kinase, in response to external signals (see Figure 19-25). 

Smooth muscle myosin contains two myosin light chains. Phosphorylation of the regulatory light chain by myosin light chain kinase is a mandatory step to induce contraction. 

Smooth muscle. The primary regulation of smooth muscle contraction occurs via phosphorylation of the Ser 19 -OH group in the 20-kDa regulatory light chains of each myosin The phosphorylated... 

The calcium mediated contraction of smooth muscle, which unlike striated muscle does not contain troponin, is quite different and requires a particular calcium-binding protein called calmodulin. Calmodulin (CM) is a widely distributed regulatory protein able to bind, with high affinity, four Ca2+ per protein molecule. The calcium—calmodulin (CaCM) complex associates with, and activates, regulatory proteins, usually enzymes, in many different cell types in smooth muscle the target regulatory proteins are caldesmon (CDM) and the enzyme myosin light chain kinase (MLCK). As described below, CaCM impacts on both actin and myosin filaments. 

Interest in the biochemical mechanisms of smooth muscle developed alongside the study of contraction in nonmuscle systems that expanded in the 1960s. It became apparent that the contracto-regulatory system of smooth muscle exhibited more basic similarities to nonmuscle systems than to those of striated tissue. A further stimulus was provided by reports (Perrie et al, 1972,1973) of the phosphorylation of the light chain of striated muscle myosin, which was catalyzed by a specific myosin light chain kinase (Pires et al., 1974 Pires and Perry, 1977). A phosphatase involved in the de-phosphorylation of the phosphorylated light chain... 

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