Synthesis of amino acid using a flow-type microreactor containing enzyme-mesoporous silica microsphere composites

A flow-type microreactor containing composite materials of a theanine synthetase (glutaminase) and mesoporous silica with 23.6 nm pore diameter (SBA-15 microsphere) was developed for the continuous synthesis of L-theanine, a unique amino acid. Enzyme-immobilisation ability and enzymatic activity in the SBA-15 microsphere with large mesopores were higher than those of SBA-15 with a 5.4 nm pore diameter. Moreover, the glutaminase-SBA-15 microsphere composites displayed higher selectivity in theanine production than the free enzyme did in a batch experiment. A direct visualization of composites of fluorescently labelled glutaminase and SBA-15 microsphere immobilised in the flow channel of the microreactor by a combination of differential interference contrast and fluorescence microscopy revealed that the enzymes were uniformly dispersed throughout the mesoporous silica particles, because of the successful encapsulation of the enzyme. The enzyme-encapsulated microreactor exhibited a high conversion of L-glutamine to L-theanine with local control of the reaction temperature. In addition to this advantage of the microreaction system, the microreactor enabled the on-off regulation of enzymatic activity during continuous theanine synthesis by controlling the reaction temperature or the pH of the substrate solution.