Addition of Tb3+ to purple membrane (PM) suspensions changes the orientation of the menbrane normal from parallel to perpendicular with respect to the magnetic field. Residual dipolar couplings measured in protein L in the presence of PM are scaled by a factor of -1/2. NMR line broadening and cross-correlation effects induced by the addition of PM are partially reversed by Tb3+ but not by Tm3+ that has no effect on the orientation of PM. This is interpreted as the result of anisotropically restricted motion of protein L in the transiently PM-bound form. Copyright © 2002 American Chemical Society.
Bernadó, P., Barbieri, R., Padrós, E., Luchinat, C., & Pons, M. (2002). Lanthanide modulation of the orientation of macromolecules induced by purple membrane. Journal of the American Chemical Society, 124, 374-375. https://doi.org/10.1021/ja0170192