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 H 2 O 2 ) 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.