Improvements of Acinetobacter radioresistens lipase adsorption on Celite 535 by adding salts

The zeta potential of Celite 535 powder in deionied water can be effectively increased by the addition of salts, especially the divalent ion Ca⁺⁺ or Mg⁺⁺. However, this enhancement was not observed in a sodium phosphate buffer near neutral pH, which implies that Ca⁺⁺ or Mg⁺⁺ can not compete with Na⁺ having adsorbed on the support surface. Improvements of the protein and lipase adsorption on Celite 535 were found when salts were added to the crude enzyme solution. The highest specific activity of 167% of the support (c.a. 2.5-fold enhancement by comparing with that without adding salts) was found when the enzyme solution contains 100 mM NB₄Cl. An S-shape adsorption isotherm for the lipase activity was found, which was attributed to the larger pores of the support. However, no purification effect was observed when the protein and lipase was precipitated by adding acetone to the enzyme solution containing 100 mM NH₄Cl.