Irradiation by electrons of tubulin solution in vitro causes tubulin assembly in absence of a magnesium cofactor

It was shown that irradiation of a tubulin solution (5 x 10(-6) mol/l) with electrons makes tubulin assemble to microtubules. The response of the system was monitored by the femtosecond laser technique. The assembly under these conditions occurs without Mg2+ (magnesium cofactor) and GTP. At 730 (the first harmonic) and 365 nm (the second harmonic), a rise in signal intensity occurs during the first 60-70 ns followed by the onset of tubulin assembly to microtubules, which was registered by the methods of spectrophotometry and electron spectroscopy. Theoretically this effect can be explained by the appearance of hydrated electrons in the solvated tubulin shell. Hydrated electrons are mostly in a long-living polaron state, which can be considered as an ensemble of quasi-dipoles of the electron-H3O+ type. The interaction of quasi-dipoles with the weak internal electrostatic field of tubulin leads, due to nonlinear effects, to a manifold rise in the intensity of the electrostatic field of the solvated shell of initially nonpolymerized tubulin chains. Finally, the increased field makes separate tubulin chains aggregate to microtubules. The effect observed is identical to the action of Mg2+ on the GTP site of beta-tubulin, which transfers it to a slightly perturbed triplet state.