Initial protein concentration effects on precipitation by salt.

The influence of initial protein concentration on the performance of salting-out precipitation is examined. In the precipitation of bovine albumin by ammonium sulfate, a peak occurs in the plot of protein solubility versus initial protein concentration; that is, the solubility first increases and then falls with increasing initial protein concentration. 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, because it covers all possible alternatives; namely, the solubility is independent of, increases with, decreases with, or first increases and then decreases with the initial protein concentration. The appearance of a solubility peak can be explained based on the occurrence of a primary particle during the precipitation process. However, inclusion of the influence of initial protein concentration into the Cohn equation is not feasible with the use of a logarithmic scale, which does not sensitively reflect the change in protein solubility. Increasing initial protein concentration favors protein recovery because it reduces the resultant volume of the supernatant phase. (c) l997 John Wiley & Sons, Inc.