Key points are not available for this paper at this time.
Fourier analysis of the thermally excited undulations of fluorescence-labelled actin filaments allowed for the first time wave-vector-dependent measurements of the bending elastic modulus kc. At wave vectors q > 2 · 106 m-1, scaling behaviour characteristic for bending undulations is clearly observed yielding a bending modulus of kc = (4.0 ± 0.4) · 10-27 Jm (corresponding to a persistence length Lp = 0.5 μm). For decreasing wave vector q the filament stiffness increases continuously. The wave-vector-dependent filament stiffness explains the differences of the persistence length as determined by static end-to-end distance measurements (Lp = (6 ± 25) μm) and by dynamic techniques (e.g., rheology and quasi-elastic light scattering) yielding Lp = 0.5 μm. The filaments exhibit occasional bends which are attributed to defects in the double-stranded threads. Binding of tropomyosin leads to a decrease of the measured bending elasticity to kc = (1.11 ± 0.09) · 10-27 Jm for wave vectors q > 2 · 106 m-1. The course of the wave vector dependence of the bending stiffness remains the same.
Käs et al. (Wed,) studied this question.