Key points are not available for this paper at this time.
Light-scattering intensities are reported of solutions containing bovine serum albumin (BSA = 2) and the polymer polyethylene glycol (PEG = l), the latter of molecular weights 1,000, 7,500, 19,000, and 100,000.With multicomponent light-scattering theory, the low concentration limits of the thermodynamic interaction parameter, apz/acl, have been calculated from these results for the three PEG samples of lowest molecular weight.The value of apz/acl for PEG of molecular weight 1,000 is in reasonable agreeement with the value calculated from published equilibrium dialysis experiments (Atha, D., and Ingham, K. (1981) J Biol.Chem 256, 12108-12177).With c1 expressed as w/v, apz/acl decreases with increasing polymer molecular weight.This trend is the opposite of that predicted on the basis of the effectiveness of PEG as a protein precipitant, which increases with increasing polymer molecular weight.Radiolabeled low molecular weight PEG was found to distribute equally between the two phases, both liquid, formed from mixtures with high concentrations of BSA and high molecular weight PEG.The presence of low molecular weight PEG in the proteinrich phase can qualitatively account for the relative ineffectiveness of low molecular weight PEG as a precipitant.The experimental values of apz/ac, for BSA
Knoll et al. (Sun,) studied this question.