The Diamagnetic Susceptibility of the Tubulin Dimer

Abstract EN

An approximate value of the diamagnetic anisotropy of the tubulin dimer, Δχdimer, has been determined assuming axial symmetry and that only the α-helices and β-sheets contribute to the anisotropy.

Two approaches have been utilized: (a) using the value for the Δχα for an α-helical peptide bond given by Pauling (1979) and (b) using the previously determined anisotropy of fibrinogen as a calibration standard.

The Δχdimer≈4×10-27 JT−2 obtained from these measurements are similar to within 20%.

Although Cotton-Mouton measurements alone cannot be used to estimate Δχ directly, the value we measured, CMdimer=1.41±0.03×10-8 T−2cm2mg−1, is consistent with the above estimate for Δχdimer.

The method utilized for the determination of the tubulin dimer diamagnetic susceptibility is applicable to other proteins and macromolecular assemblies as well.