Glucose oxidase apoenzyme

Examples of surface-immobilized mediators are electropolymerized azines for electro-oxidation of The extreme form of this approach is formation of biocatalytic monolayer, comprising a surface-bound mediator species that is itself bound to a single enzyme molecule. Katz et al. report a complete cell based on novel architecture at both electrodes (Figure 7). On the anode side, the FAD center of glucose oxidase is removed from the enzyme shell and covalently attached to a pyrroloquinoline quinone (PQQ) mediator species previously immobilized on a gold surface. The GOx apoenzyme (enzyme with active center removed) is reintroduced in solution and selectively binds to FAD, resulting in a PQQ-... 

S108 Morris, D.L. (1985). Effect of antibodies to glucose oxidase in the apoenzyme reactivation immunoassay system. Anal. Biochem. ISl, 235-241. 

A variation of the EMIT is the apoenzyme reconstruction immunoassay system, where the analyte is coupled not to the enzyme itself but to a cofactor or prosthetic group that is required for enzyme activity. For example, the analyte may be coupled to flavin-adenine dinucleotide (FAD), which is required for glucose oxidase activity. The antibody binds to the FAD-analyte conjugate and prevents FAD from interacting with the enzyme, whose activity is consequently reduced. The more analyte present in the sample, the more competition there is for the antibody and the more FAD-analyte conjugate remains free in solution and available to the enzyme. Again, the level of enzyme activity is related to the quantity of analyte in the sample. 

Comparative c.d. studies for Aspergillus niger D-glucose oxidase and the corresponding apoenzyme suggested that the FAD co-enzyme is not a gross structural determinant of the enzyme. ... 

A cofactor (or coenzyme) may be immobilized on an insoluble support at the same time as an enzyme, provided that it forms an undissociable unity with the apoenzyme. For example, during the production of a glucose electrode, FAD (flavin adenine dinucleotide) is bound to glucose oxidase and does not require supplementary immobilization. 

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