Actine loopbanden

Actin treadmilling is the continuous addition of G-actin monomers at F-actin's plus-end and the simultaneous removal from the minus-end. At steady-state, this keeps the filament length unchanged but allows the newly added actin monomers to move forward within the filament.

Treadmilling depends on the critical concentration or C_c of the free monomer, which is the concentration at which the rates of polymerization and depolymerization are equal.

The actin filament grows if the free monomer concentration is higher than the C_c and shrinks if it is lower.

During actin treadmilling, the monomer concentration remains in between the C_c values for the plus and minus-ends, allowing faster and continuous addition of ATP-G-actins only at the plus-end.

These ATP-G-actin monomers undergo gradual ATP hydrolysis with slow phosphate release, resulting in three different forms of actin within F-actin: ATP-actin, ADP-phosphate-actin, and ADP-actin.

The ADP-actins are weakly bound and readily dissociate, resulting in continuous depolymerization at the minus-end of F-actin.