Non-physiological redox couples

There are several requirements for an "ideal protein system for such studies [68-70]. First, in order to facilitate structure vs. function comparisons, the proteins studied should be of known structure. This structure may be obtained, for example, by high-resolution X-ray spectroscopy. Second, physiological redox protein couples are preferred, since such systems are more likely to provide information on biological design than studies of non-physiological redox couples. Third, for practical purposes, it is... 

Recently, biosensors have been developed which use a non-physiological redox couple to shuttle electrons between the FADH2 and the electrode by the following mechanism ... 

Ferrocene may be employed in biosensors,as a non-physiological redox couple, to shuttle electrons between the biological component and the electrode. The high reversibility and low redox potentials, make It more desirable than the more common natural acceptors for the oxidases, such as oxygen, for facilitating electron transfer. Sensors based on the ferrocene/ferricinium redox couple have been previously reported [11,12,13]. 

Turning to one-electron couples in Fig. 2, the reduction of oxygen to superoxide is clearly more difficult than subsequent one-electron reductions, with a redox potential of —0.33 V It must be emphasized however, that standard conditions, i.e., PO2 = 1 atm and [O -] = 1M, are non-physiological. In most mammalian cells, one should expect a reduction potential is C /O -] close to 0.2 V, which means that the formation of superoxide in such cells is much easier than in standard conditions [24,32]. The one-electron reduction of oxygen is performed by many semiquinones, SQ - [33], according to ... 

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