The molecular weight of Cp(−10)149d was determined under nondenaturing conditions (50 mM NaHPO4 buffer, pH 7.2). The open circles represent experimental data and the solid line represents a curve fitted using a single-species model. The upper panel shows the residuals (difference between the fitted and experimental values) as a function of radial position. The molecular weight determined (37,500) is close to that predicted (36,000) for a stable dimer. In the example shown, the Cp(−10)149.C48A.C107A mutant was used. Similar results were obtained for the other Cp(−10)149d constructs described including one, for example, with solubility enhancing mutations G123A.R127A.15