INTERACTIONS OF ADENOSINE TETRAPHOSPHATE WITH MYOSIN AND ACTOMYOSIN

Myosin-ATPase prepared from dog heart and rabbit skeletal muscle catalyzed the hydrolysis of adenosine tetraphosphate into adenosine diphosphate and orthophosphate. Maximum activities were measured in the presence of Ca++ ions and represented 15 to 50% (according to pH and to origin) of the maximum activities measured in the presence of adenosine triphosphate (ATP). Low activities were measured in the presence of Co++ > Ni++ > Mg++ ions. Actomyosin-ATPase prepared from rabbit and from carp muscles hardly catalyzed the hydrolysis of adenosine tetraphosphate (2. 5% of the rate of ATP hydrolysis) in the presence of Mg++ ions at low ionic strength. Ultracentrifugation analysis showed that carp muscle actomyosin is split into actin and myosin by low concentrations of adenosine tetraphosphate whereas the contaminating ATP or the ATP formed from adenosine tetraphosphate during the centrifugation does not markedly influence the centrifugal pattern.