The calculation of some physical parameters of proteins from sucrose density gradient centrifugation data

A simplified procedure is described for the calculation of protein physical parameters from data obtained by sucrose density gradient centrifugation. The position of an uncharacterized protein relative to standard proteins is determined after centrifugation through linear 5-20% sucrose gradients prepared in both H2O and D2O. From these data, together with the density of each 5% sucrose buffer, the partial specific volume and standard sedimentation coefficient can be calculated without knowledge of rotor dimensions, angular velocity, time of centrifugation, or solvent viscosity. In the absence of specific solvent-induced changes in protein composition or conformation, the magnitude of error due to the approximations inherent in the method is estimated to be less than 2.3% in partial specific volume or less than 10-15% in sedimentation coefficient.