FLEXURAL RIGIDITY OF MICROTUBULES MEASURED WITH THE USE OF OPTICAL TWEEZERS

The flexural rigidity of single microtubules is measured using optical tweezers. Two new methods are presented. In both the optical forces o f the laser trap are used to directly manipulate microtubules grown of f the ends of Chlamydomonas axonemes. The shapes of the microtubules a re observed by video microscopy as the hydrodynamic forces of viscous flow counteract the elastic restoring forces when the microtubules are moved actively relative to the surrounding buffer medium. To determin e the flexural rigidity, the bending of a microtubule is analyzed unde r a given velocity distribution along its length. Microtubules incubat ed with taxol after polymerization are measured to be more flexible th an those without taxol added. On the other hand, MAPs are shown to inc rease microtubule stiffness.