Studies on Enzymatically Active Subfragments of Myosin-Adenosine Triphosphatase

Abstract

An enzymatically active subfragment was isolated from heavy meromyosin and also from myosin aggregate after the chymotryptic digestion at low temperature. The adenosine-triphosphatase (EC 3. 6. 1. 3) activity in the presence of C²⁺ was 1.0μ mole of P₁ liberated per mg protein per min. The molecular weight of this subfragment was about 1.0×10⁵. The two properties were indistinguishable from those of sub-fragments prepared by using other proteolytic enzymes. In the presence of F-actin, however, the adenosine-triphosphatase activity of this subfragment was considerably higher than that of other subfragments. Actin polymerization was accelerated by this subfragment as heavy meromyosin does, while it was not accelerated by the subfragment prepared by the tryptic digestion.