Fig. 1.

Example for the change of equilibrium profile as a function of rotor speed in a multi-speed sedimentation equilibrium (SE) experiment and the benefit from implicit mass conservation constraints. A set of three samples in a dilution series of mixtures of a natural killer cell receptor fragment and its binding partner, the major histocompatibility complex class I protein (Dam et al. 2006) were brought to SE sequentially at rotor speeds of 15,000, 20,000, and 25,000 rpm and scanned at 280 and 250 nm. Shown are representative radial absorbance profiles of one sample acquired at 250 nm (symbols) and best-fit distributions (solid lines). Global fitting parameters were the macroscopic binding constants and the loading molar ratio of components common to all samples; local fitting parameters for each cell were the dilution factors of each sample and the best-fit bottom position (meniscus and bottom are represented in the plot as the limits of the abscissa). In the global analysis of three cells, the implicit mass conservation (Vistica et al. 2004) reduced the number of fitting parameters reflecting unknown protein concentrations from 18 to 4