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°C. 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 ( 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 [1]. 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 (B ) with the solubility of lysozyme in a binary mixture.