On the stiffness of the natural actin filament decorated with alexa fluor tropomyosin.

Natural, phalloidin-free, actin filaments were decorated with tropomyosin made fluorescent by reaction with alexa fluor (R) 488 C(5) maleimide. The elastic modulus by stretching of these filaments was then determined and found to span between 38.2 MPa and 61.48 MPa. We tried also to determine the yield strength of the same filaments in the laser light trap operated at 920 mW, the maximum power of the apparatus. Only two out of the 10 filaments tested were broken under these conditions, yield strength being 50.5 and 55 pN, respectively.