Electron transfer reaction of glucose oxidase hybrids modified with phenothiazine via poly(ethylene oxide) spacer on acidic amino acid residues

GOx hybrids [GOx-(PT-PEO-NH₂)] are prepared by covalently bonding phenothiazine(PT)-labeled poly(ethylene oxide) (PEO) oligomers having an amino end group, PT-PEO-NH₂, to acidic amino acid residues on the enzyme surface. The rate constant for the mediated FADH/FADH₂ oxidation calculated from the catalytic current under substrate-saturated conditions ranges from 1.7 to 388 s^-1, and the largest value is obtained for GOx hybrids with PT-PEO of molecular weight 3000. Surprisingly effective electron transfer from FADH/FADH₂ to PT⁺ is achieved in the GOx-(PT-PEO-NH₂) hybrids due to the PT modification to aspartic or glutamic acid residues, many of which are located close to the FAD center.