Fig. 4. Proximal leg segment is a monomer at pH 6.2 in an equilibrium sedimentation assay. Proximal leg was expressed and purified and its self-interaction was assessed by equilibrium sedimentation in a Beckman XL-I analytical ultracentrifuge at 40K r.p.m., 4°C, pH 6.2. WinNonLin was used to simultaneously fit data points from samples of 0.4 (left), 0.2 (center), and 0.1 mg/ml (right) at 7K (green), 10K (orange), and 14K (purple) to the lines shown in black. (Radial distance)²/2 (R^{^}2/2) is plotted against A280 (AU). A plot of the residuals (lower panel) indicates the systematic error in the fit between the lines and the raw data points. The fit gave values for parameter σ = 0.623 (0.547–0.696) where for the expected monomer σ = 0.667. The fit is consistent with a proximal leg segment fitted to an N-mer of N = 0.94, which represents monomer. Variance of fit was 4.6 × 10^–5 with 1234 degrees of freedom.