Study On Selective Biotransformation Of (R)-(-)-Mandelic Acid Using Immobilized Nitrilase

Crude nitrilase was purified at pH 7.0 using membrane separation technology, Freeze- dried nitrilase with high activity (69U) could be obtained by use of 0.5% sucrose as cryoprotectants. It can be know that purified nitrilase was oligomeric enzyme with a 21190Da molecular weight. The optimal conditions of catalytic reaction are as follows: pH value is 9.6, the mass ratio between enzyme and substrate is 7:10, and temperature is 40℃. Enzyme activity was increased in water-toluene system with a pahse ratio of 1:10. In order to improve catalytic efficiency, 717 resin was added in water phase to adsorb and separate R-mandelic acid.In the presence of condensation agent DCC, crossinked D155–lysine resin (L-D155) was prepared through the condensation reaction. The immobilized nitrilase was prepared through crosslinking method with the D155-lysine resin as the immobilization carrier. Amide bond and schiff base were separately found in D155–lysine resin and immobilized nitrilase by means of IR, demonstrating nitrilase was successfully immobilized on D155 resin through lysine.The optimal conditions of immobilization are as follows: the molar ratio among glutaraldehyde, amino group of L-D155 and nitrilase is 0.11:1:1.72×10^-4, pH 5.25, resulting in coupling ratio of 43.2%, 10 15U of enzyme activity, Thermal stability increased. It maintenance 85% activity after 5 times repeated use.