The diamagnetic susceptibility of the tubulin dimer.
An approximate value of the diamagnetic anisotropy of the tubulin dimer, Δχ dimer, 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 Δχ α for an α -helical peptide bond given by Pauling (1979) and (b) using the previously determined anisotropy of fibrinogen as a calibration standard. The Δχ dimer ≈ 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(-2)cm(2)mg(-1), is consistent with the above estimate for Δχ dimer. The method utilized for the determination of the tubulin dimer diamagnetic susceptibility is applicable to other proteins and macromolecular assemblies as well.
Netherlands Organisation for Scientific Research, Dutch-Belgian Beamlines, European Synchrotron Radiation Facility, BP 220, 38043 Grenoble, France.
Wim
0000-0001-5070-4039
W
Bras
Netherlands Organisation for Scientific Research, Dutch-Belgian Beamlines, European Synchrotron Radiation Facility, BP 220, 38043 Grenoble, France.
James
J
Torbet
Science and Technology Facility Council (STFC), Daresbury Laboratory, Cheshire WA4 4AD, UK.
Gregory P
GP
Diakun
National Centre for Scientific Research (CNRS), National High Magnetic Field Laboratory, 143 Avenue de Rangueil, 31400 Toulouse, France.
Geert L J A
GL
Rikken
CIB Centro de Investigaciones Biológicas, Ramiro de Maeztu 9, 28040 Madrid, Spain.
J Fernando
JF
Diaz