Enzymatic Preparation of L-Malate in a Reaction System with Product Separation and Enzyme Recycling

Reaction coupling separation systems using calcium fumarate as a substrate can break the reaction equilibrium and promote the production of L-malate. However, the low reusability and stability of fumarase limit its further application. In this study, partially purified fumarase of Thermus thermophilus (87.0 U mg(-1)) was immobilized within konjac-K-carrageenan beads. An amalgamation of konjac and carrageenan gum (2%) was used to form the beads, and polyethylene polyamine (0.2%) and glutaraldehyde (0.1%) were used as the cross-linking agents. The pH and temperature profiles of free and immobilized fumarases were remarkably similar. The diffusion limit of immobilized fumarase caused a decline in the maximal velocity (V-max), whereas the kinetic constant (K-m) value increased. Optimization of the parameters for biotransformation by immobilized fumarase showed that 88.3% conversion of 200 mM calcium fumarate could be achieved at 55 degrees C within 8 h. The beads were stored for 30 days at 4 degrees C with minimal loss in activity and were reusable for up to 20 cycles with 78.1% relative activity. By recycling the reaction supernatant, a total amount of 3.98 M calcium fumarate was obtained with a conversion of 99.5%, which is the highest value ever reported.