Abstract
Work on the biochemistry of smooth muscle has revealed that myosin is responsible for the Ca2+ regulation of smooth muscle contraction. Phosphorylation of myosin light chains was required for contraction and dephosphorylation of the phosphorylated light chains was required for relaxation. The role of Ca2+ was to activate myosin light chain kinase which phosphorylates the myosin light chains. Thick filaments of smooth muscle myosin were readily disassembled upon addition of ATP, to a myosin monomer with a sedimentation coefficient of approximately 10S. 10S-myosin was quite different in the molecular conformation and enzymatic activity from a myosin monomer (6S-myosin) formed in 0.3 M of higher concentrations of KCl. The ATP-induced changes were strongly inhibited by phosphorylation of light chains. In this review, the data on the structure and function of 10S-myosin were summarized.
