Kinetic investigations of 6-phosphogluconate dehydrogenase confined in mesoporous silica

• Immobilization of G.s.6PGDH onto alkyl and aminoalkyl modified MCFs is possible.
• Immobilization is initiated due to hydrophobic interactions.
• Activity retention is highest when employing a 0.5 mg mL−1 6PGDH solution for immobilization.
• The stability of the immobilized 6PGDH shows a dependency on the spacer length.
• Investigation of the Michaelis-Menten kinetics proposed a C5-chain as optimal spacer.

In this study 6-phospogluconate dehydrogenase (6PGDH) from Geobacillus stearothermophilus was adsorbed onto the inner surface of mesoporous cellular siliceous foams (MCF). To initiate different attractive interactions between the surface of 6PGDH and the respective silica hosts, the pore walls of the MCFs have been functionalized with alkyl and aminoalkyl residues consisting of different chain lengths (–C3, –C5, –C7, –C11 and –C3NH2, –C5NH2, –C7NH2, –C11NH2). Each modified MCF has been analyzed by nitrogen physisorption, thermal analysis as well as zeta potential titrations. Enzyme uptakes, loading densities, long-time stabilities, leaching as well as enzyme kinetics were investigated. So far kinetic investigations of enzymes immobilized onto mesoporous silica hosts are rare although kinetics give important information about diffusional resistance of substrate or coenzyme. In fact 6PGDH immobilization leads to an increase of the Michaelis-Menten constants (Km) for the substrate and the coenzyme. The enzyme efficiency for 6PGDH immobilized on the surface of aminoalkyl functionalized MCF is larger than the value gained for the enzyme on alkyl functionalized materials.

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