Myosin-mediated Ca++-regulation of actomyosin-adenosinetriphosphatase from porcine aorta.

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Abstract
The nature of the Ca2+-sensitive regulatory system for contraction of vascular smooth muscle is considered in detail. Smooth muscle actomyosin prepared from the medial layer of porcine aorta is analyzed chemically and its ATPase (EC 3.6.1.14) activities are investigated. The Mg2+-ATPase of this vascular actomyosin is sensitive to the concentration of Ca in the range from 0.1 mM-10 nM. The Ca sensitivity is maintained in the presence of excess pure actin from skeletal muscle and is abolished in the presence of pure skeletal myosin. The regulatory properties of this natural actomyosin from smooth muscle are in the myosin portion of the protein complex and are not bound to actin-tropomyosin as in skeletal muscle.