Disassembly and reconstitution of the Ca2+-sensitive thin filaments of vascular smooth muscle

AbstractThe Ca2+-sensitive thin filaments of aorta smooth muscle have been, disassembled into their constituent proteins, actin, tropomyosin and a 120-kDa protein. The 120-kDa protein bound to aorta actin-tropomyosin and inhibited its ability to activate myosin MgATPase. This inhibition correlated with the binding of one 120-kDa protein molecule per 29 actin monomers. Upon the addition of calmodulin to the actintropomyosin-120-kDa protein complex, the inhibition was relieved in 10−4 M Ca2+ but not 10−9 M Ca2+. The full release of inhibition was not accompanied by a full release of 120-kDa protein binding to actintropomyosin. A fully active, Ca2+-sensitive aorta thin filament has thus been reconstituted from just four components: actin, tropomyosin, 120-kDa protein and calmodulin