Naturally occuring, potent regulator of actin polymerization present in human platelets at a concentration of 200 - 500 μM. Sequesters G-actin monomers in a 1:1 ratio (Kd = 0.7 - 1.0 μM) and allows rapid filament polymerization in the presence of profilin. Implicated in wound healing, induction of MMPs, chemotaxis, angiogenesis, inflammatory processes and tumor progression.