Effect of phosphates on the structure of the actin filament

The fine structure of the purified actin filament was investigated by negative staining. The actin filament polymerized in Tris-HCl buffer and KCl showed a collapsed image different from that of a double stranded helix. Addition of ATP, ADP, or inorganic orthophosphate, however, converted it into a straight filament with typical double strands.