Enzymatic hydrolysis of ATP and e-ATP by F-actin

Enzymatic hydrolysis of e-ATP by F-actin with and without application of sonic vibration at various pHs was investigated and compared with that of ATP. There was no significant difference on enzymatic activity between F-actin-bound e-ADP and F-actin-bound ADP. The hydrolysis rate of e-ATP under sonic vibration decreases monotonically with decreasing pH, similar to that of ATP. The magnitude of e-ATP hydrolysis rate was, however, about one third of that of ATP hydrolysis rate in the pH range between 6.3 and 8.5. Enzymatic hydrolysis of e-ATP without sonic vibration at room or higher temperatures decreases monotonically with increasing pH and becomes almost negligible at pH 8.5. The pH profile and the magnitude of enzymatic hydrolysis without sonic vibration were similar with ATP. Since the fluorescence intensity of e-ATP at 410 nm is enhanced by the binding with G-actin, the exchange binding affinity of e-ATP to G-actin which can be measured fluorophotometrically was about one third of that of ATP.