Peroxidases metal induction

Table 6-1. Metal induction of peroxidase in different organs of higher plant species (after Van Assche and Clijsters, 1990b, adapted).

Trace metals, particularly copper, cobalt, and iron, greatly increase the rate of LO and influence the direction of peroxide decomposition [72], These metals function both to reduce the induction period and increase reaction rate by decomposing hydroperoxides. Trace levels of these catalysts, e.g., as little as 0.3 ppm iron or 0.01 ppm copper, will result in prooxidant effects [73]. Iron may exist in foods in the free form or as a part of an enzyme (contain organically bound haem, Fe+ or haemin, Fe+ ). Enzymes containing haematin compounds include catalase and peroxidase (plant tissues) and haemoglobin, myoglobin, and cytochrome C (animal tissues). While heat treatment results in denaturation of the enzymes, it frees the iron to greatly enhance its catalytic properties. This is particularly relevant in the formation of warmed-over off-flavor in cooked meats. 

The induction of DNA strand breaks and chromosomal aberrations by cadmium in mammalian cells was suppressed by antioxidants and antioxidant enzymes, indicating the involvement of ROS [34—36], Since the extent of ROS and damage to cellular macromolecules depends on the equilibrium between their generation and detoxification or repair, respectively, the occurrence of oxidative DNA damage is assumed to be due to an inhibition of the antioxidant defense by cadmium, such as the antioxidant enzymes catalase, superoxide dismutase, glutathione reductase, and glutathione peroxidase. One other mechanism proposed consists in the displacements of redox active metal ions, e.g., Fe ", for example in metallothionein, giving rise to Fenton reactions [35-37]. 

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