The hydrolysis of ATP that accompanies actin polymerization is essentially irreversible

Abstract
The hydrolysis of ATP that accompanies the polymerization of actin occurs on the F-actin subsequent to the addition of the G-ATP-actin subunit to the elongating filament. We now show that this ATP hydrolysis is essentially irreversible. Thus, a large decrease in free energy occurs at the cleavage step, F-ATP-actin → F-ADP-Pi-actin.