Functional immobilization of racemase by adsorption on folded-sheet mesoporous silica

Alanine racemase from Geobacillus stearothermophilus was physically immobilized on folded-sheet mesoporous silica (FSM) with pore diameters of 4 or 8.5 nm, and the activity, thermal stability, and reusability of the racemase were examined. The FSM with the larger pore diameter showed greater immobilization of the racemase, probably because its pores are large enough to adsorb the enzyme in the inner pore. The immobilized racemase retained 51% activity relative to that of the free enzyme in both the l-alanine (l-Ala) to d-Ala and d-Ala to l-Ala reactions. The racemase also exhibited a predominant thermal stability, and was successfully reused at least six times when immobilized on FSM. These results indicate the potential utility of FSM as an immobilization support for enzymes.