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Protein salting-out: phase equilibria in two-protein systems
C J Coen1, J M Prausnitz, H W Blanch
1Department of Chemical Engineering, University of California, Berkeley, California 94720-9989, USA.
Biotechnology and Bioengineering
|March 20, 1997
Summary
Protein interactions in salt solutions were studied. Lysozyme-ovalbumin mixtures showed unique phase behavior due to pH-dependent association, unlike lysozyme-chymotrypsin mixtures.
Area of Science:
- Biochemistry
- Physical Chemistry
- Protein Science
Background:
- Protein solubility in aqueous solutions is influenced by factors like pH, ionic strength, and protein-protein interactions.
- Understanding the phase behavior of binary protein mixtures is crucial for applications in biotechnology and food science.
Purpose of the Study:
- To investigate the phase behavior of binary protein mixtures (lysozyme-chymotrypsin and lysozyme-ovalbumin) in ammonium sulfate solutions.
- To determine how protein concentration, pH, and ionic strength affect the phase separation of these mixtures.
- To elucidate the role of protein-protein association in modulating phase behavior and solubility.
Main Methods:
- Preparation of aqueous binary protein mixtures (lysozyme-chymotrypsin and lysozyme-ovalbumin).
- Addition of ammonium sulfate to induce phase separation.
- Quantification of protein concentrations in coexisting phases.
- Systematic variation of pH and ionic strength to study their effects.
Main Results:
- Lysozyme-chymotrypsin mixtures exhibited phase behavior similar to individual proteins, with minimal influence from the second protein.
- Lysozyme-ovalbumin mixtures displayed distinct phase behavior compared to single-protein systems.
- The association between lysozyme and ovalbumin was observed to be dependent on pH and ionic strength.
- Protein association was identified as a critical factor governing protein solubility in salt solutions.
Conclusions:
- The phase behavior of binary protein mixtures is not always predictable from individual protein behavior.
- Specific protein-protein interactions, like those between lysozyme and ovalbumin, significantly alter phase diagrams.
- pH and ionic strength are key parameters controlling protein association and, consequently, solubility in salting-out solutions.
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