A study of the effects of ethylenediamine-tetra-acetic acid on myosin adenosinetriphosphatase.

The trior tetrasodium salt of ethylenediaminetetraacetic acid (EDTA or Na EDTA) is a strong chelating agent for heavy metals and the alkaline earth metals, calcium and magnesium. By this action the activity of enzymes which are known to be influenced by calcium or magnesium is altered by the addition of EDTA; e.g., muscle adenylate kinase, which is accelerated by magnesium, is completely inactivated by 0.001 M EDTA (l).l Slater and Cleland stabilized a-ketoglutaric oxidase of heart muscle sarcosomes by additions of EDTA, an action which they attribute to the removal of deleterious calcium which enters sarcosome suspensions (2). Altman and Crook found that horse heart succinoxidase is greatly activated by EDTA, an activat,ion which can also be produced by phosphate and chromate or by purifying the substrate and enzyme (3). Gross, working at low ionic strength, found that the adenosinetriphosphatase (ATPase) activity of mouse heart homogenate was strongly inhibited by EDTA at 0.004 to 0.01 M, but at 0.001 to 0.003 M the activity was 150 per cent that of untreated homogenates (4). Using myosin B as ATPase, we found that the rate of dephosphorylation was decreased by EDTA at 0.05 M KC1 (5). On the other hand, Friess observed that EDTA accelerates the ATPase activity of myosin B 400 per cent at 0.6 M KC1 and pH 7 (6). It has now been confirmed by Friess and us that these opposite effects of EDTA were dependent upon the concentration of KCl. Since this corroboration, we have explored the effect of triNa EDTA upon the ATPase activity of myosin A and myosin B over a wide range of concentrations of KC1 and have done the other experiments indicated by the section titles in response to queries which arise from consideration of the marked acceleration of myosin ATPase by EDTA.