INITIAL PROTEIN-CONCENTRATION EFFECTS ON PRECIPITATION BY SALT

The influence of initial protein concentration on the performance of s alting-out precipitation is examined. In the precipitation of bovine a lbumin by ammonium sulfate, a peak occurs in the plot of protein solub ility versus initial protein concentration; that is, the solubility fi rst increases and then falls with increasing initial protein concentra tion. in addition, the dependence of solubility on the initial protein concentration is less significant if using higher salt concentrations . The solubility behavior of bovine albumin may be representative, bec ause it covers all possible alternatives; namely, the solubility is in dependent of, increases with, decreases with, or first increases and t hen decreases with the initial protein concentration. The appearance o f a solubility peak can be explained based on the occurrence of a prim ary particle during the precipitation process. However, inclusion of t he influence of initial protein concentration into the Cohn equation i s not feasible with the use of a logarithmic scale, which does not sen sitively reflect the change in protein solubility. Increasing initial protein concentration favors protein recovery because it reduces the r esultant volume of the supernatant phase. (C) 1997 John Wiley & Sons, Inc.