Glucose oxidase photoswitchable

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... 

Willner I, Blonder R, Katz E. Reconstitution of apo-glucose oxidase with a nitrospiro-pyran-modified FAD cofactor yields a photoswitchable biocatalysts for amperometric transduction of recorded optical signals. J Am Chem Soc 1996 118 5310-11. 

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. 

Willner, I., Katz, E., Willneg B., Blondei R., Heleg-Shabtai, V., and Buckmann, A. F. Assembly of functionalized monolayers of redox proteins on electrode surfaces novel bioelectronic and optobioelectronic systems. Biosens. Bioelectron. 1997,12, 337-356. Blonder R., Katz, E., Willneg I., Wray, V., and Buckmann A. F. A lication of a nitro-spiropyran-FAD reconstituted glucose oxidase and cfuurged electron inediators as optobioelectronic assemblies for the amperometric transduction of recorded cortical signals control of the ON - OFF direction of the photoswitch. J. Am. Chem. Soc. 1997, 119, 11747-11757. 

M. Lion-Dagan, S. Marx-Tibbon, E. Katz, and I. Willner, Photoswitchable electrical communication of glucose oxidase and glutathione reductase with electrode surfaces through photoisomerizable redox mediators, Angew. Chem. Int. Ed. Engl. 34, 1604-1606 (1995). 

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.

Although the trans to cis photoisomerization of merocyanins leads to a reversible cyclization reaction (see Chapter 2), use of these photoswitchable motifs may be mentioned herein. A photoisomerizable FAD analog was employed to modify glucose oxidase in such a way that electron transfer resulting from glucose oxidation occurs in the spiropyran form and not in the merocyanin form, probably due to the variation of positioning of the FAD moiety [142]. 

A photoswitchable bioelectrocatalytic device based on a similar azo-SAM with a PAA-g-CD coating was designed, able to catalyze the oxidation of glucose by glucose oxidase upon inclusion of ferrocene-methanol (Fc), as electron mediator, into the available free CD units of the PAA-g-CD film. Photoreversible activation and deactivation of the enzyme could be obtained by UV/Vis light irradiation. The immobilization and release of the redox polymer was driven by the trans-cis photoisomerization of the azobenzene units in the SAM. ... 

Photostimulation of redox enzymes could transduce recorded optical signals as an amperometric response by their electrical interaction with electrode interfaces. For example, amperometric transduction of recorded optical signals was accomphshed using nitrospiropyran-modified glucose oxidase as photoswitchable material (Fig. 44) [14]. 

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