Effect of surfactant agents and lipids on optical resolution of amino acid by ultrafiltration membranes containing bovine serum albumin

Ultrafiltration experiments for the optical resolution of racemic phenylalanine were performed in a solution system containing bovine serum albumin (BSA) and surfactant agents (Triton X-100, Tween 20, sodium dodecyl sulfate), lipid (phosphatidylcholine) and fatty acid (palmitic acid sodium salt). It was found that D-phenylalanine preferentially existed in the permeate at pH 7.0 due to the binding of BSA to L-phenylalanine in the feed and that the separation factors (= concentration ratio of D-isomer to L-isomer in the permeate) increased with a decrease in the BSA solution containing no additives and in the BSA solution containing Triton X-100 or Tween 20. The unusual tendency that the separation factors were less than unity was observed and the separation factors decreased with a decrease in the feed concentration of phenylalanine during the ultrafiltration containing the palmitic acid sodium salt or the phosphatidylcholine. This is caused by the fact that the binding constants of D-phenylalanine to BSA are higher than those of L-phenylalanine in the BSA solution containing the palmitic acid sodium salt or phosphatidylcholine. Since there were found conformational changes of BSA in the presence of palmitic acid sodium salt based on circular dichroism measurements of BSA solution, the conformational changes of BSA were attributed to the higher affinity of D-phenylalanine to BSA than that of L-phenylalanine in the BSA solution containing the palmitic acid sodium salt or phosphatidylcholine.