Analytical ultracentrifuge for the characterization of detergent in solution

We have characterized the hydrodynamic behaviour in H2O and D2O of two detergents, dodecyl-beta-D-maltoside (DDM) and octaethylene glycol monododecyl ether (C12E8), by analysing sedimentation velocity profiles obtained with interference optics in terms of continuous particle distribution and non-interacting species. The analysis in H2O provides values for the sedimentation and diffusion coefficients that give aggregation numbers of 130 and 115 for DDM and C12E8, respectively, close to that given in the literature. The analysis of the number of interference fringes as a function of detergent concentration gave values for the critical micelle concentration and refractive index increments that are also in good agreement with published values. The values of the partial specific volumes of DDM and C12E8, obtained by sedimentation in H2O and D2O - where C12E8 floats - are identical to those obtained from density measurements. These results indicate that sedimentation velocity has good potential for proper characterisation of detergent-solubilized proteins.