EFFECT OF COEXISTING AMMONIUM-SULFATE ON CHARACTERISTICS OF PAPAIN ULTRAFILTRATION

The salting-in and salting-out of protein result from the variation of state of protein in the solution with the concentration of coexisting salt. These phenomena are encountered in the ultrafiltration of protein dissolved in an aqueous salt solution. The ultrafiltration of an aqueous papain solution containing ammonium sulfate of various concentrations was carried out in a stirred vessel. Although the papain concentrations in the bulk liquid were much lower than its solubilities and the variation in viscosity of solutions was small, the characteristics of ultrafiltration varied with ammonium sulfate concentration. For a given papain concentration the resistance of the gel layer increased with increasing ammonium sulfate concentration in the salting-out region. In the salting-in region the mass transfer coefficients were large and the concentrations of papain at the interface of the gel layer were near the solubilities. In the salting-out region the former were small and the latter were higher than the solubility. The results suggest that papain behaves as molecules in the salting-in region but as aggregates in the salting-out regions.