Oxygen detoxification pathway

Figure 5 (A) Evidence that paraquat transiently affects chloroplasts of resistant Conyza and (B) that there are constitutively elevated levels of the Halliwell-Asada active oxygen detoxification pathway in the chloroplasts. A. Resistant and susceptible plants of Conyza bonariensis were sprayed to runoff with 0.1 mM paraquat and whole leaves were removed for measurement of photosynthesis at times thereafter as an estimation of paraquat arriving at, and affecting chloroplasts. Simultaneous measurements of stomatal aperture were made to ascertain that the stomates remained open. Source Data redrawn from (60). B. Normal enzyme levels (without paraquat treatment) in resistant and susceptible Conyza bonariensis. Source Collated and drawn from (57, 61).

Table 1. Herbicide cross tolerances to oxidative stresses and relations with enzymes of the Halliwell-Asada active oxygen detoxification pathway [cf. 36-39]...

Nearly all ischemic events are modulated by temperature, and cerebroprotection from hypothermia is believed to increase resistance against multiple deleterious pathways including oxidative stress and inflammation [205-211]. Generally, most biological processes exhibit a of approximately 2.5, which means that a 1°C reduction in temperature reduces the rate of cellular respiration, oxygen demand, and carbon dioxide production by approximately 10% [212]. Reduced temperature also slows the rate of pathological processes such as lipid peroxidation, as well as the activity of certain cysteine or serine proteases. However, detoxification and repair processes are also slowed, so the net outcome may be complex. Hence, hypothermia appears to be an attractive therapy that targets multiple injury mechanisms. 

Fig. 11 Biochemical pathways for the formation, detoxification, and cellular effects of xenobiotic free radical intermediates and reactive oxygen species (ROS). Fe iron, G-6-P glucose-6-phos-phate, GSH glutathione, GSSG glutathione disulfide, H2O2 hydrogen peroxide, FIO hydroxyl radical, LPO lipoxygenase, NADP nicotinamide adenine dinucleotide phosphate, O2 superoxide, P450 cytochromes P450, PHS prostaglandin H synthase, SOD superoxide dismutase. (Modified from Wells et al. 1997)...

Cytochrome P-450s are the best-known class of hydroxylation enzyme. Their active sites contain a heme iron that forms a highly activated oxygenating species that reacts by a radical mechanism. In higher animals, they function primarily in metabolite degradation as part of pathways that clear unnatural substances such as toxins and drugs. Hydroxylation inaeases polarity that facilitates further derivatization by other detoxification enzymes or excretion of the hydroxylated products. Other P-450 family members are involved in secondary metabolite biosynthesis, particularly in plants and microbial cells (Figure 1.6). 

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