There is a strong link between solubility, and thus crystallisation, and the molecular interactions of proteins in dilute salt solutions. Such molecular interactions are governed by the weak interaction forces (electrostatic, hydration and hydrophobic). In this work molecular interactions were determined and correlated with solubility for the enzyme, alpha-amylase from Bacillus licheniformis (BLA) which finds an important application in starch hydrolysis.

Molecular interactions were determined using self interaction chromatography (SIC) which evaluates the second virial coefficient (B₂₂). The second virial coefficient was found to be highly dependent on the pH, salt type and salt concentration. Strong molecular interactions were observed at high (>1.2 M) salt concentration in ammonium sulphate solutions. Correspondingly salting-out behaviour was observed during solubility experiments, strongly supporting the usefulness of the second virial coefficient in predicting the crystallisation behaviour of enzymes in salt solutions.