Phosphorylating electron-transferring

Oxidative Phosphorylation Electron transfer through the cytochrome system liberating free energy which is transformed into high-energy phosphate bonds. [NIH]... 

A similar inconsistency exists concerning oxidative phosphorylation in AD. Although activities of enzymes of the mitochondrial electron transfer chain are reported to be normal in AD brain, partial uncoupling of oxidative phosphorylation (electron transfer and phosphorylation of adenosine diphosphate are normally functionally linked) (Sims et al., 1987) and overexpression of cytochrome oxidase subunit-3 gene in cerebral temporal cortices (Alberts et al., 1992) have been reported. In addition, substantial decreases of complex IV activity were detected in platelets from five patients with AD (Parker et al., 1990). 

Structural problems in oxidative phosphorylation Electron transfer... 

We saw in Case studies 4.2 and 4.3 that exergonic electron transfer processes drive the synthesis of ATP in the mitochondrion during oxidative phosphorylation. Electron transfer between protein-bound co-factors or between proteins also plays a role in other biological processes, such as photosynthesis (Section 5.11 and Case study 12.3), nitrogen fixation, the reduction of atmospheric Nj to NH3 by certain microorganisms, and the mechcuiisms of action of oxidoreductcises, which are enzymes that catalyze redox reactions. 

Dinitrophenol is a member of the aromatic family of pesticides, many of which exhibit insecticide and fungicide activity. DNP is considered to be highly toxic to humans, with a lethal oral dose of 14 to 43mg/kg. Environmental exposure to DNP occurs primarily from pesticide runoff to water. DNP is used as a pesticide, wood preservative, and in the manufacture of dyes. DNP is an uncoupler, or has the ability to separate the flow of electrons and the pumping of ions for ATP synthesis. This means that the energy from electron transfer cannot be used for ATP synthesis [75,77]. The mechanism of action of DNP is believed to inhibit the formation of ATP by uncoupling oxidative phosphorylation. 

Fig. 6.9 The catalysts for denitrification. Nitrate is reduced by a molybdenum enzyme while nitrite and oxides of nitrogen are reduced today mainly by copper enzymes. However, there are alternatives, probably earlier iron enzymes. The electron transfer bct complex is common to that in oxidative phosphorylation and similar to the bf complex of photosynthesis, while cytochrome c2 is to be compared with cytochrome c of oxidative phosphorylation. These four processes are linked in energy capture via proton (H+) gradients see Figure 6.8(a) and (b) and the lower parts of Fig. 6.9 which show separately the active site of the all iron NO-reductase, and the active site of cytochrome oxidase (02 reductase).

Complex I can be regulated by phosphorylation. Demin et al. [28] studied superoxide generation by Complex III using the kinetics model of electron transfer from succinate to cytochrome c. 

Electron transfer dissociation (ETD) is an ECD-like method with most of the same characteristics [21]. Like ECD, ETD yields abundant peptide backbone c- and z-type ions while often retaining such labile groups as peptide O/TV-glycosylation and phosphorylation [22]. Unlike ECD, ETD can be performed in the presence of an RF field. Here, anions created in a chemical ionization (Cl) source (see Section 2.1.7) are used as electron donors but the fragmentation pathways are essentially the same as for ECD. Commercial linear QIT instruments have recently become available with the ETD option. 

The driving force of oxidative phosphorylation is the difference between the electron transfer potential of NADH or FADH2 relative to that of 02. For the redox couple... 

It is considered [7,11] that directed transition of protons serves as energy source during phosphorylation. Between the numbers of transported protons and electrons certain stoichiometric relations are revealed. Thus, in the course of electron transfer (along the whole transport system) ATP molecules are formed. 

Apparently, ATP phosphorylation energy can also be estimated through the system of electron transfer. 

ASPECTS OF CARBOHYDRATE OXIDATION, ELECTRON TRANSFER, AND OXIDATIVE PHOSPHORYLATION... 

This was confirmed by Keilin and Hartree using antimycin A as an inhibitor. The antibiotic blocked the reduction of cytochrome cx by NADH or succinate but did not block the reduction of cytochrome b. This site-specific inhibition brought antimycin A into popular use by biochemists in the analysis of electron transfer and oxidative phosphorylation. 

The spatial separation between the components of the electron transport chain and the site of ATP synthesis was incompatible with simple interpretations of the chemical coupling hypothesis. In 1964, Paul Boyer suggested that conformational changes in components in the electron transport system consequent to electron transfer might be coupled to ATP formation, the conformational coupling hypothesis. No evidence for direct association has been forthcoming but conformational changes in the subunits of the FI particle are now included in the current mechanism for oxidative phosphorylation. 

The major role of electron transfer is the generation of ATP from ADP and P, (oxidative phosphorylation). Since the... 

Coupling of electron transfer with oxidative phosphorylation... 

In any cell that depends on aerobic metabolism, if the rate of ATP utilisation increases, the rate of the Krebs cycle, electron transfer and oxidative phosphorylation must also increase. The mechanism of regulation discussed here is for mammalian skeletal muscle since, to provide sufficient ATP to maintain the maximal power output, at least a 50-fold increase in flux through the cycle is required so that the mechanism is easier to study (Figure 9.22). 

Figure 9.25 Control of the Krebs q/cle and myosin-ATPase by direct effects of Ccf ions and the resultant effects on electron transfer and oxidative phosphorylation in muscle. The stimulation of the Krebs cycle by ions results in an increase in the NADH/NAD concentration ratio, which stimulates electron transfer. The stimulation of myosin-ATPase by Ca lowers the ATP/ADP concentration ratio, which also stimulates electron transfer. The Ca ions are released from the sarcoplasmic reticulum in muscle in response to nervous stimulation. In addition, generation of ADP by myosin ATPase increases the ADP concentration, which stimulates the cycle. Note that a lack of oxygen will prevent generation of ATP (Chapter 13).

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