Myosin and Contractile Activity in Smooth Muscle
In relaxed smooth muscle the contractile apparatus is dormant and the initiation of contraction requires an activation. It is generally agreed that the activation is achieved by phosphorylation of the two 20,000-dalton light chains of myosin (LC20) and usually Serine 19 is phosphorylated. This process is catalyzed by myosin light chain kinase (MLCK) and the Ca2+-dependence of the system is due to the activation of the MLCK apoenzyme by the Ca2+4 calmodulin (CaM) complex. Dephosphorylation and inactivation of the contractile apparatus, reflects the activity of a light chain phosphatase. The latter, however, has not been well characterized and it is not known, for example, if one or more phosphatases are involved or, if the phosphatase activity is regulated.
KeywordsATPase Activity Myosin Head Smooth Muscle Myosin Cross Bridge Chicken Gizzard
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