Abstract
1. At low ionic strength, when turbidity and viscosity measurements indicated dissociation of acto-heavy-meromyosin, its adenosine triphosphatase was strongly activated by Mg2+ and Ca2+. 2. The characteristics of the adenosine triphosphatase of dissociated acto-heavy-meromyosin in the presence of Mg2+ were similar to those reported for myofibrils and actomyosin. 3. In the presence of Ca2+ the adenosine-triphosphatase activity was much less sensitive to ionic strength than was the case with Mg2+. 4. At low ionic strength Mg2+ was more effective in maintaining the dissociation of acto-heavy-meromyosin in the presence of ATP than was Ca2+. This difference was not apparent when ATP was replaced by ITP. 5. Although the recovery of viscosity was complete on reassociation of acto-heavy-meromyosin the turbidity did not return to the original value. 6. The general implications of Mg2+ activation of acto-heavy-meromyosin when classical interpretation indicates dissociation of the complex are discussed.
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Selected References
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