Liquid crystal polymorphism in F-actin: Optical microscopic and rotatory dispersion studies

Filamentous actin (F-actin), which occurs abundantly and ubiquitously in li ving mechanisms such as muscle, nonmuscle cells, and cytoskeleton, exhibits a liquid crystal polymorphism as its concentration is increased. The doubl e-stranded, helical F-actin filaments are 1-70 mu m long in our samples. Th e chirality of the filaments is consistent with the experimental observatio n of the characteristic cholesteric fingerprint and uniform textures. In ad dition to the chiral nematic phase, our optical microscopic studies show th e occurrence of tilted chiral smectic phases, e.g., smectic C*, I*, or F*, and a smectic B phase. Measurement of optical rotatory dispersion in the ch olesteric phase confirms the prediction of the de Vries equation describing the optical rotatory dispersion behavior for cholesterics. The observed ly otropic polymorphism is consistent with the Flory lattice model and a semif lexible polymer mesogen model of F-actin. (C) 1999 American Institute of Ph ysics. [S0021- 9606(99)50841-6].