Redox coenzymes potential electron transport chain

Electron transport chain Present in the mitochondrial membrane, this linear array of redox active electron carriers consists of NADH dehydrogenase, coenzyme Q, cytochrome c reductase, cytochrome c, and cytochrome oxidase as well as ancillary iron sulfur proteins. The electron carriers are arrayed in order of decreasing reduction potential such that the last carrier has the most positive reduction potential and transfers electrons to oxygen. 

Reversed electron transport reversal of Oxidative phosphorylation (see) in which NAD is reduced by an ATP-dependent reverse transport of electrons. R.e.t. occurs in organisms that oxidize hydrogen donors whose redox potential (see Oxidation) is more positive than that of the pjmdine nucleotide coenzymes, and it operates in the oxidation of substrates not specific for NAD (see Respiratory chain), e.g. Succinate + NAD - Fumate + NADH + H. Tlie redox system succinate/fumarate (E o = -tO - 031V) is 325 mV more positive than the redox system NAJD / NADH + H (E o =-0.32 V) electrons are passed firom succinate to flavoprotein in the respiratory chain, then via NADH-dehydrogenase to NAD. R.e.t. has been shown in nitrate bacteria (Nitrobac-ter), insect flight muscle mitochondria and kidney mi-... 

NADH and FADHg are produced as a result of substrate level dehydrogenations. Oxidation of these reduced coenzymes by oxygen is accomplished by the intervention of a series of electron carriers between the primary reductant and the terminal oxidant (Fig. 2). The electron-transport components represent redox couples of increasing redox potential and are therefore favored thermodynamically. The respiratory chain can be separated into four multienzyme complexes NADH-Q reductase (complex I), succinate-Q reductase (complex II), QH2"Cytochrome c reductase (complex III), and cytochrome c oxidase (complex IV). At each of these successive oxidation-reduction steps, a certain amount of free energy is available, the amount being determined by the difference in the oxidation-reduction potential of the two sequential components. The difference in the redox potential between... 

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