Abstract
1) A preparation containing actin-like protein was extracted from the smooth muscle of the intestine with the use of STRAUB'S method.
2) The viscometric observation suggested that intestinal actin-like proteinseemed to act as a monomer (globular actin) in salt-free solution and topolymerize to some polymer (fibrous actin) when low KCl was added.
3) The extent and speed of viscosity-rise, following the polymerization, wereaccelerated by the addition of 0.4 mM ATP and a minute amount of ultra-sonicated skeletal F-actin.
4) This protein formed a complex with skeletal myosin A which behavessimilarly to the actomyosin from skeletal muscle in ATPase activity andphysico-chemical properties.
5) Ultracentrifugal analysis showed that this actin-like preparation is com-posed of three components. One of them, the main component, showed asedimentation constant of about 30 S which was equivalent to that of skeletalF-action. Sedimentations of the other two components were about 50 and 4-7S. respectively.
6) From the above results, it may be concluded that a main protein of theactin-like preparation obtained is globular actin. Some properties of intestinal actin were discussed by comparing it with those of skeletal actin.
