A series of glucose oxidase (GOx) hybrids (GOx-phenothiazine-labeled poly(ethylene oxide) (PT-PEO)) capable of direct electrical communication with electrodes is synthesized by covalently modifying PT-PEO to lysine residues on the enzyme surface. The length of the PEO chain and the number of PT groups are systematically altered. After the PT-PEO modification, all the hybrids maintain more than 50% of enzyme activity relative to that of native GOx, although loss of the activity becomes greater with increasing PEO chain length. The catalytic current, icat, is observed at a potential more positive than 0.55 V after the addition of glucose, due to the intramolecular electron transfer (ET) from reduced forms of flavin adenine dinucletide (FADH2/FADH) to PT+ that are electrogenerated at the electrode. The icat value increases with the number of PT groups, indicating that most of the modified PT groups act as mediators. The magnitude of the icat increase depends on the PEO chain length and reveals a maximum for PT-PEO with the molecular weight of 3000. In contrast, the icat is almost constant for GOx-2-(10-phenothiazyl)propionic acid (PT-PA) hybrids with more than two PT groups synthesized by covalently modifying PT-PA to surface lysines, indicating that only a few key PT groups function as mediators. The maximum rate constant (130 s-1) for the ET from FADH2/FADH to PT+ is obtained for the GOx hybrid modified with five PT-PEO groups with the molecular weight of 3000.
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