Interactions of proteins in aqueous ammonium-sulfate solutions:Mixtures of lysozyme and ovalbumin Page: 3 of 28
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egg-white protein is lysozyme and 60% is ovalbumin (Hegg, 1979; Awad6 et al., 1994). These
two proteins have been studied extensively in connection with the processing of eggs in the food-
processing industry (Rossi and Schiraldi, 1992) under conditions (e.g., high temperature) that
denature proteins. Judge et al. (1995) crystallized ovalbumin to a purity of 99% from aqueous
ammonium sulfate containing a mixture of ovalbumin, conalbumin and lysozyme. Lysozyme has
been selectively precipitated from lysozyme-ovalbumin mixtures at high pH and ammonium
sulfate ionic strength (Coen et al., 1997). At a mole ratio of 3:1 (lysozyme:ovalbumin), Jeffrey et
al. (1979) found a maximum in solution turbidity for low ionic strength near neutral pH. The
authors postulated that a complex containing three lysozymes for each ovalbumin would give the
lowest solubility. This postulate may correspond to either a 3:1 ratio of associated
lysozyme:ovalbumin (leading to a highly insoluble complex), or to an indefinite association of
lysozyme and ovalbumin, where four lysozymes are coordinated with each ovalbumin and
lysozyme can bind to two ovalbumin molecules.
Fluorescence anisotropy and ultracentrifugation results have shown that the equilibrium
constant for a 1:1 lysozyme-ovalbumin association ranges from 0.3 to 1.1 X 105 M1 in 20-mM
sodium-phosphate buffer at pH 6.8 (Clarke and Howlett, 1979; Nakai and Kason, 1974). Nakai
and Kason (1974) showed that the association between lysozyme and ovalbumin was highly
dependent on pH and ionic strength up to 0.3 M; this suggests that the association at low ionic
strength is primarily driven by the electrostatic interactions of the oppositely charged lysozyme
and ovalbumin. These electrostatic attractions are screened at moderate ionic strengths.
In this work, we measure the fluorescence anisotropy as a function of ammonium-sulfate
ionic strength for mixtures of lysozyme and ovalbumin at 25 C and pH 7 to obtain the lysozyme-
ovalbumin cross association constants. The effective lysozyme-ovalbumin potential of meanAnderson et al., 3
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Anderson, Camille O.; Prausnitz, John M. & Blanch, Harvey W. Interactions of proteins in aqueous ammonium-sulfate solutions:Mixtures of lysozyme and ovalbumin, report, November 10, 2001; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc792724/m1/3/: accessed March 28, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.