Xp105dr

Density and specific gravity of solutions were measured on a DMA 5000 density meter at 20.001°C (Anton Paar). Proteins were dialyzed with six exchanges against 4 liters of water over three days before measurements. After measurements, solutions were weighed, dried, and reweighed on a balance (XP105DR; Mettler Toledo). Specific volume (inverse of specific gravity) was plotted against percent protein mass (weight protein/weight solution) similar to what was done with BSA (Bernhardt and Pauly, 1975 (link)), but as suggested by Lewis and Randall (1961) . The partial specific volume is extrapolated at 100% protein from either a linear fit or a tangent to the curve if the data are nonlinear, but a partial specific volume is desired for a specific range of protein concentration. With the molecules we studied, the data are linear through attainable concentrations. The errors were determined by propagation of error for density measurements and mass measurements. Partial specific volume of the SKp/CaM complex was measured at each concentration with fourfold molar excess Ca²⁺. Corrections and controls for added Ca²⁺ were applied for mass and density measurements. Measurements are included in Table 1.