Redox mediators phenazine methosulfate

Scheme 11. Idealized sketch showing the electroen matic oxidation of L-lactate at gold modified electrode surfaces, (a) Lactate dehydrogenase bound to CB-terminated alkylthiol SAMs prepared by covalent attachment of CB to 3-mercaptopropionic acid SAM derivatized with 1,4-diaminobutane. The electroenzymatic oxidation of lactate is observed only in the presence of soluble coenzyme (NAD" ") and a redox mediator (phenazine methosulfate) [215]. (b) Lactate deh3tdrogenase bound to NAD-terminated alkylthiol SAMs prepared by covalent attachment of Af -(2-aminoethyl)-NAD to a cystamine SAM derivatized with pjrrroloquinoline quinone. The reconstituted enzyme is electrically wired to the electrode surface via two NAD" -binding pockets involved in the affinity-binding surface reaction [242].

Gardner et al. [165] have shown that the redox-cycling agent phenazine methosulfate (PMS), mitochondrial ubiquinol-cytochrome c oxidoreductase, or hypoxia inactivated aco-nitase in mammalian cells. It has been proposed that the inactivation of aconitase is mediated by superoxide produced by prooxidants because the overproduction of mitochondrial MnSOD protected aconitase from inactivation by the prooxidants mentioned above except hyperoxia. Later on, the reaction of superoxide with aconitases began to be considered as one of the most important ways to NTBI generation in vivo. 

The OTTLSET has also been used to investigate redox proteins in addition to chytochrome c. In the case of Mb, the in situ absorption spectra with phenazine methosulfate as the mediator provide a Nernst plot with E° = -1-0.0464 V versus SHE and n = 0.95. Measurements of E° at various temperatures and with appropriate mediators have been made to determine the thermodynamic parameters of the blue copper... 

A second methanol anode was demonstrated with methanol dehydrogenase, which was mediated by one of two species phenazine methosulfate (PMS) or phenazine ethosulfate (PES) [116]. The redox potentials of these mediators are 0.08 and 0.05 V versus SCE (also shown in Figure 9.6). It can be seen that all three mediators have a large potential difference from the methanol oxidation potential. Eliminating this potential loss was an engineering problem waiting to be solved. 

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