Oxygen pathway, from peroxide

P450s are capable of utilizing an oxygen atom from peroxide to catalyze oxygen insertion without electron transport proteins or the NAD(P)H cofactor, through the peroxide shunt pathway ... 

Thromboxanes, like prostaglandins, contain a ring of five or six atoms the pathway from arachidonate to these two classes of compounds is sometimes called the cyclic pathway, to distinguish it from the linear pathway that leads from arachidonate to the leukotrienes, which are linear compounds (Fig. 21-16). Leukotriene synthesis begins with the action of several lipoxygenases that catalyze the incorporation of molecular oxygen into arachidonate. These enzymes, found in leukocytes and in heart, brain, lung, and spleen, are mixed-function oxidases that use cytochrome P-450 (Box 21-1). The various leukotrienes differ in the position of the peroxide... 

JAs are derived from linolenic acid via an octadecanoid pathway consisting of several enzymatic steps (Figure 36). Multiple compartments in plant cells participate in JA synthesis. The early steps of this pathway occur in chloroplasts, where linolenic acid is converted to OPDA by means of the three enzymes lipoxygenase (LOX), allene oxide synthase (AOS), and allene oxide cyclase (AOC).867-869 Linolenic acid is oxygenated by 13-LOX producing a peroxidized fatty acid 13-hydroperoxylinolenic acid. The product is subsequently metabolized by AOS to an unstable compound allene oxide. Allene oxide is sequentially converted by AOC to produce OPDA. An alternative pathway from another trienoic fatty acid, hexadecatrienoic acid (16 3), is present in chloroplasts.870 In this pathway, dinor OPDA is produced instead of OPDA. OPDA and dinor OPDA are transported into the peroxisome. An ABC transporter involved in this transport was identified in... 

Several 1,2-dioxolanes [7, 75-76] and polycyclic peroxides [7, 77[ have been obtained in modest yields from unsaturated hydroperoxides by peroxyl radical cyclization-oxygenation pathways under initiation with DBPO or DTBN (cf. Scheme 43) [76a, 77[. In general, there is a strong bias for exo cyclization [7a, 75b], although an exception has been noted [78]. Moreover, when there is a choice, the... 

Oxygen (O2) is the most abundant element in the Earth s crast. The oxygen reduetion reaetion (ORR) is also the most important reaction in life processes such as biological respiration, and in energy converting systems such as fuel cells. ORR in aqueous solutions occurs mainly by two pathways the direct 4-electron reduction pathway from O2 to H2O, and the 2-electron reduction pafliway from O2 to hydrogen peroxide (H2O2). In non-aqueous aprotic solvents and/or in alkaline solutions, the 1-electron reduction pathway from O2 to superoxide (O2 ) can also occur. 

The more easily oxidized dianion, possible only in dipolar aprotic solvents, succumbs to O2 alone. The reaction of the radical (or radical anion) with oxygen may lead to the endoperoxide, and thus join the pathway from the diazaquinone. Other peroxidic products leading to chemiluminescence have not been excluded. 

The second pathway is seen distinctly at mercury and graphite electrodes. These electrodes are quite inactive in the catalytic decomposition of H2O2. Moreover, at them the potential where the peroxide is reduced further is more negative than the potential where it is formed from oxygen. Hence, within a certain range of not too negative potentials, the reaction can occur in such a way that the hydrogen peroxide formed accumulates in the solution. 

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