Reactive oxygen species chemical reactivity

Hu, C. et al., Black rice (Oryza sativa L. indica) pigmented fraction suppresses both reactive oxygen species and nitric oxide in chemical and biological model systems, J. Agric. Food Chem., 51, 5271, 2003. 

That the oxidative burst is directly involved in the chemical defense of these algae is clear. This reaction can be inhibited by diphenyleneiodonium, a suicide inhibitor of NADPH-oxidase which suppresses both the production of reactive oxygen species and the natural resistance to epiphytic bacteria. In addition a role in the defense against endophytes was indicated, since pre-treatment with oligomeric guluronates resulted in decreased infection of L. digitata with the pathogen Laminariocolax tomentosoides [141]. 

Only a limited number of reliable prediction tools are currently available for photoinduced toxicity. This is not surprising since establishing phototoxic potential is a complex task. Phototoxicity can be the consequence of various mechanisms such as photogeneration of reactive oxygen species, production of toxic photoproducts or sensitization of DNA damage by energy transfer. In addition, so far, there are no available universal descriptors (indicators) to predict the photodynamic potency of chemicals. 

Another example is paraquat, which can accept an electron from donors such as NADPH, becoming a stable free radical, which is not chemically reactive. However, it will generate reactive oxygen species by donating an electron to available oxygen (see chap. 7). 

For example, chemicals such as lead (Pb2+) or stressors such as reactive oxygen species (ROS) and UV light can modulate this control. Thus, from Figure 6.11 it can be seen by stopping inhibitory control [eg. ROS which blocks action of protein phosphatases (PTP)] a chemical can be mitogenic and increase cell division. Alternatively stimulation [e.g., low concentrations of Pb2+ stimulate protein kinase C (PKC)], is also mitogenic. 

As indicated in Fig. 16.2, in addition to energy transfer, chemical reactions of excited UCs ( UC, 3UC ) may lead to the formation of other reactive oxygen species (ROS) that may react with organic pollutants. Such ROS include DOM-derived oxyl- and peroxyl radicals (RO , ROO ), superoxide radical anions (02 ) that may be further reduced to H202, and hydroxyl radicals (HO ). In the case of HO , however, DOM is a net sink rather than a source. Finally, some of the 3UC may react directly with certain more easily oxidizable pollutants (see below). 

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