Electron transport chain production

As its name implies, the citric acid cycle is a closed loop of reactions in which the product of the hnal step (oxaloacetate) is a reactant in the first step. The intermediates are constantly regenerated and flow continuously through the cycle, which operates as long as the oxidizing coenzymes NAD+ and FAD are available. To meet this condition, the reduced coenzymes NADH and FADH2 must be reoxidized via the electron-transport chain, which in turn relies on oxygen as the ultimate electron acceptor. Thus, the cycle is dependent on the availability of oxygen and on the operation of the electron-transport chain. 

During dtric add production there is massive generation of NADH but little demand for ATP. Thus the situation could quickly arise where there is no further ADP available for oxidative phosphorylation within the cells. This means that the electron transport chain cannot operate and no further oxidation of NADH can occur. 

It is important that mitochondrial oxygen radical production depends on the type of mitochondria. Recently, Michelakis et al. [78] demonstrated that hypoxia and the proximal inhibitors of electron transport chain (rotenone and antimycin) decreased mitochondrial oxygen radical production by pulmonary arteries and enhanced it in renal arteries. This difference is probably explained by a lower expression of the proximal components of electron transport chain and a greater expression of mitochondrial MnSOD in pulmonary arteries compared to renal arteries. 

Figure 6. Model of the hydrogen producing device, illustrating location and orientation of His-tagged PS1 and FS2 as engineered in this report as part of the semiartificial electron transport chain for the production of hydrogen from water.

All tissues except mature red blood cells are able to manufacture haem for use in the respiratory cytochrome proteins of the electron transport chain. However, the liver is an especially important site of haem synthesis because it (a) is a major organ of erythropoiesis in utero and (b) haem-containing cytochrome-P450 (CYP-450) enzymes play significant roles in hepatic detoxification of drugs, toxins and endogenous waste products (Section 6.4). 

Reaction 15.12 would be catalyzed by the electron-transport chain, with coupled phosphorylation, and all the oxygen in the sulfite product would be derived from water (in contrast to the oxygenase, in which two thirds of the oxygen atoms in sulfite come from dioxygen). Overall, Equations 15.11 and 15.12 produce the same result as Equation 15.10. 

The transport of electrons generated in catabolic pathways down the electron transport chain of mitochondria results in the production of essential quantities of ATP. 

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