Oxygen as an electron acceptor

Oxygen reaching the soil surface from the water column is consumed by the following biochemical 

FIGURE 6.21 Schematic showing oxidation of reduced compounds in the aerobic soil layer. 

Heterotrophic microbial respiration in aerobic soil layers, where oxygen is nsed as an electron acceptor  

Chemical oxidation of rednctants snch as rednced Fe(ll) and Mn(ll) and snllides that dif-fnsed from the anaerobic layer to the aerobic layer. These rednced componnds are the products of an alternate electron acceptor reduction during respiration by facultative anaerobes  

Lithotrophic oxidation of ammonium and methane by obligate aerobic organisms  

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Such enzymes catalyse reactions involving electron transfer. Oxidases use molecular oxygen as an electron acceptor (Scheme 10.10). Dehydrogenases remove hydrogen atoms from the substrate and transfer them to an acceptor other than oxygen. 

Aerobic Lives in the presence of oxygen and carries out oxidation reactions using oxygen as an electron acceptor... 

Vinyl chloride is the least-oxidized chlorinated aliphatic hydrocarbon, and may serve as an electron donor. A vinyl chloride molecule consists of more hydrogen atoms relative to chloride atoms (3 to 1) thus, reductive dechlorination is not favorable to biodegradation. However, under aerobic conditions, vinyl chloride can serve as an electron donor with oxygen as an electron acceptor. 

Regardless of the source, phenolic acids are ultimately broken down to gaseous products such as CO2 and methane. This breakdown occurs by three general methods (i) aerobic respiration, using molecular oxygen as an electron acceptor, the end product being CO2, (ii) anaerobic respiration with electron acceptors such as nitrate and (iii) anaerobic fermentation with phosphorylation reactions involving no external electron acceptor (50). 

In 1951, the late Alan Mehler (1951) observed that chloroplasts can use oxygen as an electron acceptor. The reaction sequence is... 

If the active site of the enzyme is located sufficiently close to the electrode surface electrons can be transferred directly from the enzyme to the electrode as depicted in Figure 5.3a. In the case of an anodic reaction, the electrode replaces the natural co-substrate (such as oxygen) as an electron acceptor. This process is known as direct electron transfer (DFT), often categorized as third-generation enzyme electrodes in the biosensor literature, and is the most elegant and simplest method of bioelectrocatalysis between an enzyme active site and an electrode. 

The term ojddase normally refers to enzymes which use molecular oxygen as an electron acceptor, generating hydrogen peroxide. 

Both donor and acceptor molecules are indispensable for the accomplishment of the photoredox reaction and the electrochemical potentials of the donor (D/D +) and acceptor (A/A" ) couples should lie within the semiconductor band gap. Oxidation reactions, photocatalysed by Ti02, are usually performed in the presence of easily reducible molecular oxygen as an electron acceptor, thereby generating a superoxide radical ion (02 ) and subsequently hydroxyl radicals. The resulting holes on the semiconductor surface can oxidize many compounds (Scheme 6.292), including alcohols, hydroxyl anion and even water.1522,1523... 

XO (Bratell ei a(., I98S Downey et at, 1988) and COx (Soussi et ai, 1989) are. sources of cytotoxic ROS. XD is converted to XO through Ca- -activated proteases, which utiiize.s molecular oxygen as an electron acceptor. The molecular oxygen is therefore reduced by XO and the... 

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