Immobilization of L-rhamnose isomerase and its application in L-mannose production from L-fructose

a constitutive L-rhamnose isomerase (L-RI) from Pseudomonas sp. strain LL172 was immobilized an various types and sizes of chitopearl beads. The highest activity yield (80%) observed was that of L-RI immobilized on chitopearl heads BCW 2603. The pH range for optimal activity and stability of the immobilized enzyme (pH 5-11) was found to be broader than that for free enzyme. The temperature for optimal activity (60 degrees C), and the thermal stability (stable at 60 degrees C for 10 min) were similar to that of the free enzyme. However, immobilized enzyme as well as free enzyme required manganese ions for maximum activity. At equilibrium, the production of L-mannose from L-fructose was determined to be 30%, and the time required to reach equilibrium was inversely proportional to the amount of immobilized enzyme added. Thus, L-mannose could be prepared on a large scale simply by increasing the initial amounts of the reaction components. Moreover, the immobilized enzyme retained about 90% of the initial activity even after five repeated uses in a batch reaction.