Catalase biological role

Although the preceding catalase biomimetic reactions are important, the true biological role of the OEC is to evolve 02 from H20. Only a few complexes evolve 02 from H20 and even fewer contain Mn (see complex 67). Perhaps the best known case is the catalytic oxidation of water by the dinuclear ruthenium complex [(bpy)2(H20)Ru0Ru(H20)(bpy)2]4+ 68, which has been well documented [9,160] and will not be discussed here. 

List the reactive oxygen species that are generated during electron transport. Explain why oxygen is a potentially toxic substance. Summarize the reactions and the biological roles of superoxide dismutase, catalase, and the peroxidases. 

The heart has a relatively low catalase activity, which, together with the superoxide dismutase (SOD) system, acts to remove hydrogen peroxide and superoxide radicals. In addition, in man, dietary vitamin C plays an important role in the reduction of vitamin E, an intrinsic antioxidant component of biological membranes (Chen and Thacker, 1986 Niki, 1987). Both vitamins C and E can also react directly with hydroxyl and superoxide radicals (HalliwcU and Gutteridge, 1989 Meister, 1992). 

Cells have substantial chemical defenses against the UV photoproducts produced in seawater and intracellular fluids. Many organisms have antioxidants (e.g., carotenoids, ascorbate, tocopherols, anthocyanins, and tridentatols) that quench photo-oxidative reactions.64-67 Cells also have enzymes (e.g., catalase and superoxide dismutase) that can counteract the oxidative nature of peroxides and other radicals.26 Some compounds, such as the UV-absorbing pigment melanin, can act as both optical filter and antioxidant.68 The MAA mycosporine-glycine (Figure 15.3) functions in a similar dual capacity.69 The role of UV-mediated reactions in seawater relative to biological effects is an important current area of study. 

Manganese is tlie third most abundant transition element 1]. It is present in a number of industrial, biological, and environmental systems, representative examples of which include manganese oxide batteries [2] the oxygen-evolving center of photosystem II (PSII) [3] manganese catalase, peroxidase, superoxide dismutase (SOD), and other enzymes [4, 5] chiral epoxidation catalysts [6] and deep ocean nodules [7]. Oxidation-reduction chemistry plays a central role in the function of most, if not all, of these examples. 

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