Immobilization by Polyurethane of Pseudomonas dacunhae Cells Containing l -Aspartate β-Decarboxylase Activity and Application to l -Alanine Production

Abstract

Whole cells of Pseudomonas dacunhae containing l -aspartate β-decarboxylase activity were immobilized by mixing a cell suspension with a liquid isocyanate-capped polyurethane prepolymer (Hypol; W. R. Grace & Co., Lexington, Mass.). The immobilized cell preparation was used to convert l -aspartic acid to l -alanine. Properties of the immobilized P. dacunhae cells containing aspartate β-decarboxylase activity were investigated with batch reactors. Retention of enzyme activity was observed to be as much as 100% when cell lysis was allowed to occur before immobilization. The pH and temperature optima were determined to be 5.5 and 45°C, respectively. Immobilized P. dacunhae l -aspartate β-decarboxylase activity was stabilized by the addition of 0.1 mM pyridoxal-5-phosphate and 0.1 mM α-ketoglutaric acid to a 1.7 M ammonium aspartate (pH 5.5) substrate solution. Under conditions of semicontinuous use in a batch reactor, a 2.5% loss in immobilized l -aspartate β-decarboxylase activity was observed over a 31-day period.