The adenosine-triphosphatase activity of dissociated acto-heavy-meromyosin.
1. At low ionic strength, when turbidity and viscosity measurements indicated dissociation of acto-heavy-meromyosin, its adenosine triphosphatase was strongly activated by Mg(2+) and Ca(2+). 2. The characteristics of the adenosine triphosphatase of dissociated acto-heavy-meromyosin in the presence of Mg(2+) were similar to those reported for myofibrils and actomyosin. 3. In the presence of Ca(2+) the adenosine-triphosphatase activity was much less sensitive to ionic strength than was the case with Mg(2+). 4. At low ionic strength Mg(2+) was more effective in maintaining the dissociation of acto-heavy-meromyosin in the presence of ATP than was Ca(2+). 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 Mg(2+) activation of acto-heavy-meromyosin when classical interpretation indicates dissociation of the complex are discussed.
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002122:Calcium Chloride / Q000494:pharmacology; D002712:Chlorides / Q000494:pharmacology; D004492:Edetic Acid / Q000494:pharmacology; D008274:Magnesium / Q000494:pharmacology; D009124:Muscle Proteins / Q000378:metabolism*; D009705:Nucleosides / Q000378:metabolism; D011817:Rabbits; D013053:Spectrophotometry
D002712:Chlorides; D009124:Muscle Proteins; D009705:Nucleosides; D000255:Adenosine Triphosphate; D004492:Edetic Acid; D000251:Adenosine Triphosphatases; D008274:Magnesium; D002122:Calcium Chloride