Actin polymerization

Assembly of actin subunits into actin filaments. An unseeded bulk reaction can show a actin nucleation lag, a growth phase and an approximately constant final polymer mass; equal endpoints need not imply equal kinetics.

A fluorescence readout of actin assembly using polymerization-dependent signal from a labelled actin fraction. Label effects, direct fluorescence changes, quenching and background must be controlled.^[ref]

The free assembly-competent actin monomer concentration at which net addition at a specified actin filament end is zero in a specified model: $C_c=k_{-}/k_{+}$. Different ends and nucleotide conditions can have different values.

Net addition of subunits at a actin filament end. A simple end model gives $v=k_{+}[G]-k_{-}$, with the sign changing at the relevant actin critical concentration.

Formation of a stable assembly from which an actin filament can grow. Lowering the concentration of assembly-competent actin monomer can affect actin nucleation much more strongly than addition to an existing end.