Photoswitching of Enzyme Activity of Horseradish Peroxidase Intercalated into Semiconducting Layers

The present study demonstrates that enzymatic reaction of horseradish peroxidase (HRP) inserted into semiconducting iron-doped titanate (FT) layers can be controlled by ultraviolet (UV) light irradiation. The resting HRP in the interlayer space is transformed into activated state (Compound I) as a result of oxidation with holes generated in the valence band of the irradiated FT layers. Subsequently, Compound I leads to the enzymatic conversion of organic substrates accompanied by two-electron reduction to regenerate the resting state. The FT layers play significant roles not only as sources of photo-oxidants (holes) for the HRP but also as UV light screeners to inhibit photodenaturation of HRP. In contrast,the titanate layer not including Fe is inappropriate as a host because of the lower absorbance of UV light. The intermittent UV light irradiation causes a clear photoswitching behavior of peroxidase activity. That is, the proposed photoinduced enzymatic reaction requires no additives such as peroxides (typically H2O2) and acidic stop solutions, which are frequently employed for batch-type operations. In the present study, advantages of the proposed technique over conventional enzymatic reaction systems are discussed in detail.