CONTRIBUTION OF PROTEIN CHARGE TO PARTITIONING IN AQUEOUS 2-PHASE SYSTEMS

Protein partitioning in aqueous two-phase systems based on phase-formi ng polymers is strongly affected by the net charge of the protein, but a thermodynamic description of the charge effects has been hindered b y conflicting results. Many of the difficulties could be because of pr oblems in isolating electrochemical effects from other interactions of phase components. We explored charge effects on protein partitioning in poly(ethylene glycol)-dextran two-phase systems by using two series of genetically engineered charge modifications of bacteriophage T4 ly sozyme produced in Escherichia coil. The two series, one in the form o f charged-fusion tails and the other in the form of charge-change poin t mutations, provided matching net charges but very different polarity . Partition coefficients of both series were obtained and interfacial potential differences of the phase systems were measured. Multi-angle laser light scattering measurements were also performed to determine s econd virial coefficients. A semi-empirical model accounting for the r oles of both charge and non-charge effects on protein partitioning beh avior is proposed, and the results predicted from the model are compar ed to the results from the experiments. (C) 1998 John Wiley & Sons, In c.