The pH Difference in Poly(Ethylene Glycol)/Citrate Aqueous Two-Phase Systems and the Influence of Sodium Chloride

Partial purification of penicillin acylase from Escherichia coli in poly(ethylene glycol)-sodium citrate aqueous two-phase systems

Studies on the partition and purification of penicillin acylase from Escherichia coli osmotic shock extract were performed in poly(ethylene glycol)-sodium citrate systems. Partition coefficient behavior of the enzyme and total protein are similar to those described in other reports, increasing with pH and tie line length and decreasing with PEG molecular weight. However, some selectivity could be attained with PEG 1000 systems and long tie line at pH 6.9. Under these conditions 2.6-fold purification with 83% yield were achieved. Influence of pH on partition shows that is the composition of the system and not the net charge of the enzyme that determines the behaviour in these conditions. Addition of NaCl to PEG 3350 systems significantly increases the partition of the enzyme. Although protein partition also increased, purification conditions were possible with 1.5 M NaCl where 5.7-fold purification and 85% yield was obtained. This was possible due to the higher hydrophobicity of the enzyme compared to that of most contaminants proteins.