Oxygen detoxification system

Figure 4. Scheme of interactions between active oxygen generating xenobiotics and the oxygen detoxification system. Light intensity, the rate constants of photogeneration of active oxygen, dissipation of the xenobiotics and the levels and rate constants of the enzymes interact to determine whether a plant will be spared or killed. 

Simultaneous direct and indirect calorimetry was applied to monitor decreased oxygen concentrations in combination with hydrogen sulphide contaminations of freshwater on two annelides, Limnodrilus hoffineisteri and Tubifex tubifex [175,176], Such combined adverse conditions are typical for polluted lakes and rivers with high organic load. Complete anoxia reduced the normoxic heat production rates (0.83 and 0.56 mW/g for L hoffineisteri and T. tubifex, resp.) to less than one fourth. Presence of 100 pmol/l H2S depressed the heat dissipation in L hoffineisteri at each oxygen level, mainly due to the strict inhibition of aerobic respiration. In contrast, heat dissipation increased in T. tubifex (up to 170 %) because of its detoxification system which protects respiration. 

Two different enzyme systems have been described, one uses cytochrome P-450 to activate oxygen whereas the other employs flavin adenine dinucleotide (FAD). Both the cytochrome P-450 and the flavin monooxygenase systems have broad substrate specificities and oxidize and oxygenate a variety of organic nitrogen or sulfur compounds. The enzymes have a widespread distribution and have been detected in animals, plants, fungi and bacteria. Their function appears to be primarily one of detoxification of xenobiotics. Microbial enzymes... 

MONOOXYGENASE An enzyme system that inserts one atom of oxygen into its substrate the various forms of cytochrome P-450 are a subset of monooxygenases. (See also DETOXIFICATION)... 

Our investigation revealed that enzymatic systems of oxygen radicals and lipoperoxides detoxification may play a leading role in the inhibition of free radical... 

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