A New Kinetic Property Characteristic of the Actomyosin-Nucleoside-Triphosphatase1

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Abstract
The nucleoside triphosphatase [EC 3.6.1.15] activity of actomyosin and that of myosin are measured by varying the concentration of nucleoside triphosphate and that of CaCl2 or MgCl2. The results thus obtained are examined by asking a question of which is responsible for the activity, the true substrate and the active enzyme in terms of the reaction scheme shown in p. 719. The answers found for the above question are summarized in Table I (see p. 720). It is emphasized that the summary (Table I) corresponds very well to the fact that myosin alone does not superprecipitate in the presence of either calcium or magnesium ions, whereas actomyosin does superprecipitate in the presence of magnesium ions and not in the presence of calcium ions. Obviously, the true substrate type of reaction scheme represents a kinetic property characteristic of the superprecipitation-coupled nucleoside-triphosphatase. It is also noted of the summary (Table I) that actin is capable of not only activating Mg-nucleoside-triphosphatase but also switching the reaction scheme from the active enzyme type to the true substrate type. It is known that trinitrophenyl-ation of myosin results in activation of the Mg-ATPase activity of myosin. However, it is now found that trinitrophenylation is not capable of switching the reaction scheme, that is to say that the Mg-ATPase reaction of trinitrophenyl-myosin stays with the active enzyme type of reaction scheme and that of acto-trinitrophenyl-myosin with the true substrate type of reaction scheme. Effect of actin on the function of myosin seems, therefore, very unique.