Photoisomerizable enzyme glucose oxidase

Scheme 8 Assembly of a photoisomerizable glucose oxidase monolayer electrode and the reversible photoswitchable activa-tion/deactivation of the bioelectrocatalytic functions of the enzyme electrode.

To optimize the photoswitchable bioelectrocatalytic features of the protein, site-specific functionalization or mutation of the active site microenvironment is essential. This was accomplished by a semisynthetic approach involving the reconstitution of the flavoenzyme-glucose oxidase with a semisynthetic photoisomerizable FAD cofactor (Scheme 9).1511 The photoisomerizable nitrospiropyran carboxylic acid (24) was covalently coupled to N6-(2-aminoethyl)-FAD (25), to yield the synthetic photoisomerizable nitrospiropyran-FAD cofactor 26a (Scheme 9(A)). The native FAD cofactor was removed from glucose oxidase, and the synthetic photoisomeriz-able-FAD cofactor 26a was reconstituted into the apo-glucose oxidase (apo-GOx), to yield the photoisomerizable enzyme 27a (Scheme 9(B)). This reconstituted protein... 

A further approach to controlling electrical communication between redox proteins and their electrode support through a photo-command interface includes photo stimulated electrostatic control over the electrical contact between the redox enzyme and the electrode in the presence of a diffusional electron mediator (Scheme 12).[58] A mixed monolayer, consisting of the photoisomerizable thiolated nitrospiropyran units 30 and the semi-synthetic FAD cofactor 25, was assembled on an Au electrode. Apo-glucose oxidase was reconstituted onto the surface FAD sites to yield an aligned enzyme-layered electrode. The surface-reconstituted enzyme (2 x 10-12 mole cm-2) by itself lacked electrical communication with the electrode. In the presence of the positively charged, protonated diffusional electron mediator l-[l-(dimethylamino)ethyl]ferrocene 29, however, the bioelectrocatalytic functions of the enzyme-layered electrode could be activated and controlled by the photoisomerizable component co-immobilized in the monolayer assembly (Figure 12). In the... 

Photoswitchable electrical communication between enzymes and electrodes has also been achieved by the application of photoisomerizable electron-transfer mediators [195, 199]. DilTusional electron mediators (viologen or ferrocene derivatives) were functionalized with photoisomerizable spiropyran/merocyanine units. These mediators can be reversibly photoisomerized from the spiropyran state to the merocyanine state (360 < A < 380 nm) and back (A > 475 nm). An enzyme multilayer array composed of glutathione reductase or glucose oxidase was electrically contacted only when the photoactive group linked to the redox relay (viologen or ferrocene derivative, respectively) was in the spiropyran state. 

Figure 3-30. Organization of a photoswitchable glucose oxidase electrode for the bioelectrocatalyzed oxidation of glucose (A) The synthesis of the photoisomerizable nitrospiropyran-FAD cofactor. (B) The reconstitution of apo-glucose oxidase, apo-GOx, with the photoisomerizable FAD-cofactor (20a). (C) The assembly of the reconstituted photoisomerizable GOx on an electrode surface and the photoswitching of the bioelectrocatalytic function of the enzyme electrode in the presence of ferrocene carboxylic acid (21) as mediator.

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