Heat denaturation of rabbit skeletal G-actin in the presence of ATP

Heat treatments at pH 7-5 induced the polymerisation of G-actin without the addition of KCl or MgCl₂. This heat-induced polymerisation of G-actin was accompanied by the splitting of ATP. The polymerised actin at 45°C could be depolymerised by dialysis against a solution containing ATP. Electron microscopic observation of actin showed that irregular filaments were formed after heat treatment at 45°C for 3h, and at 55°C small filamentous pieces were formed. The abilities of heavy meromyosin ATPase (EC 3.6.1.32) activation and ATP splitting of G-actin were drastically impaired by heating to temperatures above 50°C. Studies of the temperature dependence of fluorescence and viscosity data also revealed that heat denaturation of G-actin in the presence of ATP occurred steeply between 45°C and 55°C.