Terminal oxidases mammalian

Extensive work by Cheah (121, 122, 123, 128, 130), mainly with M. expansa, has shown that large cestodes possess a cytochrome chain which differs from the mammalian system in being branched and possessing multiple terminal oxidases (Fig. 5.11). One branch resembles the classical chain with cytochrome a3 as its terminal oxidase. The terminal oxidase of the alternative pathway, which branches at the level of rhodoquinone or vitamin K, is an o-type cytochrome. Cytochrome o is an autoxidisable b-type cytochrome which is commonly found in micro-organisms, parasitic protozoa and plants. The classical chain constitutes about 20% of the oxidase capacity in cestodes and cytochrome o is quantitatively the major oxidase. Cyanide-insensitive respiration - i.e. where oxygen uptake occurs in the presence of cyanide - is characteristic of most helminths (39). Cytochrome o binds cyanide much less strongly than cytochrome a3, and it seems reasonable, therefore, to equate cyanide-insensitive respiration with the non-classical pathway. 

Copper plays an important role in the constituents of many enzymes of the mammalian organism as well as in plants and anthropods. Several classes of oxidizing enzymes for copper have been described, including the cytochrome oxidases which are the terminal oxidases in the mitochondrial electron transport system, a key reaction in energy metabolism (34), and the amine oxidases (35) of which there are a number that contain copper (36,37,38), Lysyl oxidase (39) is probably the most important since it plays a major role in elastin and collagen synthesis... 

In contrast to the mammalian succinate oxidase, this mitochondrial complex in large helminths such as F. hepatica, Ascaris lumbricoides and Monieza expansa, forms H2O2 from oxygen instead of water and is insensitive to cyanide, azide and antimyein. In addition, there is evidence that the mitochondria of these large helminths contain a functional branched respiratory chain system with two terminal oxidases cytochrome 0 and Ug. The major pathway with cytochrome o as its terminal oxidase is apparently linked with H2O2 formation (23). 

HCN is a systemic poison toxicity is due to inhibition of cytochrome oxidase, which prevents cellular utilization of oxygen. Inhibition of the terminal step of electron transport in cells of the brain results in loss of consciousness, respiratory arrest, and ultimately, death. Stimulation of the chemoreceptors of the carotid and aortic bodies produces a brief period of hyperpnea cardiac irregularities may also occur. The biochemical mechanisms of cyanide action are the same for all mammalian species. HCN is metabolized by the enzyme rhodanese which catalyzes the transfer of sulfur from thiosulfate to cyanide to yield the relatively nontoxic thiocyanate. 

Much work has demonstrated the presence of complex multienzyme monooxygenase systems within the endoplasmic reticulum of several mammalian species (for Reviews 1, 2, 3). These monooxygenase systems are responsible for the oxidative metabolism of many exogenous and endogenous substances, and the unusual non-specificity of these monooxygenase enzymes allows the metabolism of compounds with diverse chemical structures. Early work demonstrated that the terminal microsomal oxidase involved in xenobio-tic biotransformation was a hemoprotein, which has been subsequently named cytochrome P-450. 

Abstract The copper-dependent amine oxidases (CuAOs) and flavin-containing polyamine oxidases (PAOs) are involved in polyamine (PA) catabolic processes. Studies on plant CuAOs are still incomplete, whereas research on plant PAOs has advanced significantly in the past decade. The maize PAO, the best smdied plant PAO, and the barley PAOs were shown to catalyze PAs in a terminal catabolic pathway. Therefore, plant PAOs were assumed to have terminal catabolic activity, which differs from the back-conversion activity of mammalian PAOs. However, plant PAOs that have back-conversion activity are now reported. Here, studies on PAOs from the two model species Arabidopsis thaliana and Oryza sativa are compiled, and research on CuAOs is updated. Our current understanding of the roles of PAOs and CuAOs in plant development and defense responses is described. 

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