Mediator transport, involving oxygen

Biological systems. Many biological processes involve "active" or carrier-mediated transport. Two examples are oxygen transport and nerve signal transmission. A good reference for biological membrane systems Is Fendler 9). 

In addition to oxygen and carbon dioxide, gases for which carrier-mediated transport has been demonstrated include carbon monoxide (10), nitric oxide (11), sulfur dioxide (12) and ethylene (13). A system Involving simultaneous transport of carbon dioxide and hydrogen sulfide, with potential applications to sour gas treating (14) is discussed in some detail below. 

In the case of fermentation, the carbon and energy source is broken down by a series of enzyme-mediated reactions that do not involve an electron transport chain. In aerobic respiration, the carbon and energy source is broken down by a series of enzyme-mediated reactions in which oxygen serves as an external electron acceptor. In anaerobic respiration, the carbon and energy source is broken down by a series of enzyme-mediated reactions in which sulfates, nitrates, and carbon dioxide serve... 

The catalytic mechanism of NOS involves the flavin-mediated electron transport from NADPH to the terminal haem, where oxygen is bound and incorporated into NO and citrulline [33]. The relative affinity of L-arginine (Km 5 xM) compared to oxygen may give clues as to the activity of the enzyme under ischaemic and reduced L-arginine conditions. 

Ubiquinones function within the mitochondria of cells to mediate respiration process in which electrons are transported from the biological reducing agent NADH to molecular oxygen. Although a complex series of steps is involved in the overall process, the ultimate result is a cycle whereby NADH is oxidized to NAD, O2 is reduced to water, and energy is produced. Ubiquinone acts only as an intermediary and is itself unchanged. 

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