P0 data table. All values verbatim from Pollard 2016 (CSHPB review). Page numbers refer to the MinerU markdown of the PDF at ~/BookLibrary/mineru-output/pollard2016/pollard2016/auto/pollard2016.md. Use this as the single citation when a script needs an actin rate constant; do not restate values in script comments without the page reference.
1 · Monomer-level reactions (§4)
Reaction
Rate / value
Citation
ATP binding to nucleotide-free Mg-actin
k_on = 6 µM⁻¹ s⁻¹
[Pollard 2016, p.1] (De La Cruz & Pollard 1995)
ATP dissociation from Mg-actin
k_off ≈ 10⁻² s⁻¹
[Pollard 2016, p.1]
Resulting ATP K_d
nanomolar range
[Pollard 2016, p.1]
Effect of free divalent cation chelation on k_off(ATP)
Critical-concentration asymmetry is what enables treadmilling.
4 · ATP hydrolysis & Pi release on filament (§4, Fig. 3)
Quantity
Value
Citation
Mg-ATP hydrolysis on filament subunit
0.3 s⁻¹
[Pollard 2016, p.2] (Blanchoin & Pollard 2002)
Hydrolysis acceleration vs monomer
~43,000-fold (= 0.3 / 7×10⁻⁶)
[Pollard 2016, p.2]
γ-Pi dissociation half-time on filament
~6 min
[Pollard 2016, p.2] (Carlier & Pantaloni 1986)
γ-Pi dissociation rate constant
~0.003 s⁻¹
[Pollard 2016, p.2]
Pi rebinding k_on to ADP-actin filament
~2 M⁻¹ s⁻¹
[Pollard 2016, p.2]
Pi K_d (polymerized ADP-actin)
~1 mM (pH-dependent)
[Pollard 2016, p.2]
ADP-Pi-actin is therefore a long-lived intermediate with kinetics close to ATP-actin. Once Pi leaves, the subunit transitions to ADP-actin behavior (1.8 µM critical conc. at both ends).
5 · Treadmilling (§4)
Quantity
Value
Citation
Steady-state treadmilling rate
< 1 subunit / sec
[Pollard 2016, p.2] (Wegner 1976)
Mechanism
net barbed-end addition + net pointed-end loss; rate-limited by Pi-dissociation asymmetry
[Pollard 2016, p.2]
Pointed-end Pi affinity is 10× weaker than barbed-end Pi affinity (Fujiwara 2007). Pointed ends therefore expose ADP-actin (high crit. conc.) before subunits are buried, driving net dissociation there.
6 · Cellular pools (§5)
Quantity
Value
Citation
Total cellular actin
50–200 µM
[Pollard 2016, p.2]
Unpolymerized fraction
~50 % (25–100 µM)
[Pollard 2016, p.2]
Free monomer concentration
sub-µM (most bound to profilin or Tβ4)
[Pollard 2016, p.2]
Anti-fabrication notes
Pointed-end ATP-actin k_on / k_off: Pollard 2016 says “much slower” without giving the numbers in this review. Consult Pollard 1986 (already in vault as [[2026-04-23-pollard-1986-actin-rate-constants]]) or Fujiwara 2007 if exact values needed.
Pointed-end Pi affinity factor of 10: Pollard 2016 cites it as “10 times weaker than that of barbed ends” (p.2 §4). The original measurement is Fujiwara 2007 PNAS — not yet in vault. Retrieve before any model relies on the factor.
Profilin / thymosin-β4 partitioning: numbers and recipe live in [[Recipe — Profilin Thymosin-β4 Monomer Pool Partitioning]].