EFFICIENT electron transfer of redox proteins to and from their environment is essential for the use of such proteins in biotechnological applications such as amperometric biosensors and photosynthetic biocatalysts(1-3). But most redox enzymes lack pathways that can transport an electron from their embedded redox site to an electrode(4,5) or a diffusing photoexcited species(6). Electrical communication between redox proteins and electrode surfaces has been improved by aligning proteins on chemically modified electrodes(7-9), by attaching electron-transporting groups(10,11) and by immobilizing proteins in polymer matrices tethered by redox groups(12-14). Generally these methods involve contacting the enzymes at random with electron relay units, Here we report an approach that allows site-specific positioning of electron-mediating units in redox proteins, We strip glucose oxidase of its flavin adenine dinucleotide (FAD) cofactors, modify tbe latter with redox-active ferrocene-containing groups, and then reconstitute the apoprotein with these modified cofactors, In this way, electrical contact between an electrode and the resulting enzyme in solution is greatly enhanced in a controlled and reproducible way.