(506e) Effect of Other Protein on the Solubility of Hen Egg White Lysozyme

Protein
separation and characterisation are crucial challenges faced by industrial
biologists and engineers working with proteins. The key aim is to extract the
valuable protein from a broth containing a mixture of proteins in the most
efficient and economic way. In
this work salt precipitation (crystallisation) has been investigated as a
purification technique for a binary protein mixture. For the bulk recovery of a
valuable protein, a thorough understanding of the interactive effect of another
protein on the solubility of the desired protein in a mixture is essential for
successful crystallisation.

Tetragonal crystals of lysozyme
were used to estimate the solubilities in the pH range 4.0 to 5.4 in salt
concentrations from 0.2 to 0.5 M at 20^oC. To estimate the effect of
other protein, lysozyme solubilities were also measured in presence of
ovalbumin. A steep drop in solubility was observed in presence of ovalbumin in
pH range 4 to 4.5 at low salt concentration (< 0.3 M). Formation of
ovalbumin-lysozyme complexes were also observed at pH 4 in low salt
concentration. Minimum effect on lysozyme solubility was observed at high pH
(> 5.0) and salt concentration (> 0.3 M). To estimate the interaction
between lysozyme and ovalbumin in salt solutions cross interaction
chromatography (CIC) was used. Strong cross interaction was observed at low
salt concentration (< 0.3 M). This work shows the effect of ovalbumin on
lysozyme solubility and correlates the second virial cross coefficient (B₂₃)
with the solubility of lysozyme in a binary mixture.