Affinity partitioning of proteins in aqueous two-phases systems containing polymer-bound fatty acids : I. Effect of polyethylene glycol palmitate on the partition of human serum albumin and α-lactalbumin

Abstract

The partition of serum albumin between the two aqueous phases of a polyethylene glycol—dextran—water two-phase system is strongly influenced by replacing a small fraction of the polyethylene glycol by its palmitate ester. The partition of albumin is compared with the partition of polymer-bound palmitate using polyethylene glycol[1- 14C]palmitate. The data indicate that a maximum (“saturation”) effect on the partition of albumin corresponds to a binding of fewer than two palmitate groups per albumin molecule The effect on α-lactalbumin corresponds to the maximum binding of 0.5 palmitate group per protein molecule. These data do not fit the most favoured available model for affinity partitioning. The deviation can be attributed to the observation that the palmitate groups probably form micelle-type aggregates in the polyethylene glycol-rich phase at the concentrations used for albumin extraction.