Proteins peroxidase-mediated reactions

On the other hand, several ROS are highly cytotoxic. Consequently, eukaryotic cells have developed an elaborate arsenal of antioxidant mechanisms to neutrahze their deleterious effects (enzymes such as superoxide dismutases, catalases, glutathione peroxidases, thioredoxin inhibitors of free-radical chain reaction such as tocopherol, carotenoids, ascorbic acid chelating proteins such as lactoferrin and transferrin). It can be postulated that ROS may induce an oxidative stress leading to cell death when the level of intracellular ROS exceeds an undefined threshold. Indeed, numerous observations have shown that ROS are mediators of cell death, particularly apoptosis (Maziere et al., 2000 Girotti, 1998 Kinscherf et al., 1998 Suzuki et al., 1997 Buttke and Sanstrom, 1994 Albina et al., 1993). 

The flexibility of the sol-gel process allows multiple approaches to enzymatic activity monitoring. The formation of hydrogen peroxide can be followed by optical measmements using another enzymatic reaction in which the oxidation of an organic dye is catalyzed by a peroxidase (HorseRadish Peroxidase HRP), coentrapped with GOD. The presence of glucose in the solution can also be detected via electrochemical means by following the redox reactions at the active site of GOD. However, because of the steric hindrance of the protein molecule, a ferrocene mediator has to be used in order to transfer electrons from the hidden active site to the electrode. Alternatively, oxygen consumption can be measmed with a Clark electrode. The hybrid gel is deposited on a Pt cathode... 

Aromatic residues have been found in proteins at positions that probably enhance the electronic coupling in systems that have been selected by evolution for efficient ET. Examples are the tryptophan mediated reduction of quinone in the photosynthetic reaction center (31), the methylamine dehydrogenase (MADH) amicyanin system, where a Trp residue is placed at the interface between the two proteins (32), as well as the [cytochrome c peroxidase-cytochrome c] complex, where a Trp seems to have a similar function (33). 

---