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G.M. Thurston; Free Energy Model for Mixtures of Alpha and Gamma Crystallins . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2356.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To identify an accurate free energy model for alpha/gammaB crystallin mixtures. We have reported that concentrated mixtures of these crystallins can separate reversibly to form two phases at body temperature, even though gammaB alone phase separates only near 0 C, and alpha alone does not phase separate. Methods: We examined a previous model, created by Baxter, Barboy and others, for the thermodynamics and liquid structure of mixtures of spheres of dissimilar sizes. The model combines hard-core repulsion with very short-range attraction, in this case between the smaller spheres. We used energetic and geometric parameters consistent with previous work on gamma-B and alpha crystallin. We examined the compressibility route to the phase boundaries. Results: The Baxter-Barboy model yields phase boundaries that agree with the experimental observations that (i) low concentrations of alpha, near the gammaB critical point, initially raise the phase separation temperature, and (ii) successively more concentrated mixtures of alpha and gammaB, with comparable proportions of the two proteins, show phase separation at very high, and successively higher temperatures. However, the predicted phase boundaries occur at concentrations lower than those observed. Conclusions: The Baxter-Barboy model provides a useful, qualitative working model for understanding the phase boundaries of alpha/gammaB mixtures.
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