Immobilization of glucose 6-phosphate dehydrogenase in silica-based hydrogels: A comparative study

Glucose 6-phosphate dehydrogenase (G6PDH) from Leuconostoc mesenteroides catalyzes the oxidation of glucose-6-phosphate (G6P) to 6-phosphogluconate in the presence of NAD(P)+. This enzyme is part of a multistep synthetic pathway for the production of hydrogen from starch and water under mild conditions. The encapsulation of the enzyme in silica-based matrices should protect the enzyme from denaturation and serve as a first step in the development of silica-based matrices for the encapsulation of further enzymes required in the reaction system. This base formulation must be adapted to the corresponding enzyme. In this work the sol–gel method was used for the encapsulation of G6PDH in silica-gels prepared by different methods. The objective was to determine the approach which offers the highest enzymatic activity of G6PDH after encapsulation. Different routes based on alkoxysilanes, aqueous and ethylene glycol modified silanes as silica precursors were investigated. To validate the activity and stability of the encapsulated enzyme, a comparison to covalently immobilized G6PDH on amino functionalized particles via glutaraldehyde was carried out. The final goal of this project is to use the enzyme-doped gels in flow-through microreactor systems, where single or more reaction steps can be carried out in sequence. G6PDH is the first of the 13 enzymes which must be studied.