Respiratory electron transport system

Measurement of the enzyme activity of the respiratory electron transport system (ETS activity) has also been used to estimate denitrification rates in the Arabian Sea (Naqvi and Shail a, 1993) and eastern tropical South Pacific (Codispoti and Packard, 1980) denitrification zones. To measure the ETS activity a crude enzyme extract is made by grinding filtered seawater samples in a buffered medium to liberate the enzymes, after which the ETS substrates NADT1+ and NADPT1+ along with tetrazo-hum salt are added as an artificial electron acceptor. Samples are then incubated for a... 

Naqvi, S. W. A., and Shailaja, M. S. (1993). Activity of the respiratory electron transport system and respiration rates within the oxygen minimum layer of the Arabian Sea. Deep Sea Res. I. 40, 687-696. 

Bidigare, R. R., King, F. D., and Biggs, D. C. (1982). Glutamate dehydrogenase (GDH) and respiratory electron-transport-system (ETS) activities in Gulf of Mexico zooplankton. J. Plankton Res. 4, 898-910. 

Iron interactions with N sources are not limited to phytoplankton. Kirchman et al. (2003) found that the growth rate, respiratory electron transport system activity, and growth efficiency of a marine gamma proteobacterium (Vibrio hatveyi) were much lower in Fe-limited cultures grown with NOs" than when NH4+ or amino acids were suppHed as N sources. They suggested that these results may help to explain why natural bacterial communities in nitrate-rich, iron-poor HNLC areas also typically exhibit reduced growth rates and efficiencies. 

Both groups of reactions are found in bacteria (14), all higher animals (i5), and plants (16) however, oxidative phosphorylation is responsible for 90 % of the oxygen consumed (i 7). Oxidative phosphorylation is driven by the respiratory electron-transport system that is embedded in the lipoprotein inner membrane of eukaryotic mitochondria and in the cell membrane of prokaryotes. It consists of four complexes (Scheme I). The first is composed of nicotinamide adenine dinucleotide (NADH) oxidase, flavin mononucleotide (FMN), and nonheme iron-sulfur proteins 18,19), and it transfers electrons from NADH to ubiquinone. The second is composed of succinate dehydrogenase (SDH), flavin adenine dinucleotide (FAD), and nonheme iron-sulfur proteins (20), and it transfers electrons from succinate to ubiquinone 21, 22). The third is composed of cytochromes b and c, and nonheme iron-sulfur proteins (23), and it transfers electrons from ubiquinone (UQ) to cytochrome c 24). The fourth complex consists of cytochrome c oxidase [ferrocytochrome c 0 oxidoreductase EC 1.9.3.1 25)] which transfers electrons from cytochrome c to O2 26, 27). 

Before we try to understand the mechanism of oxidative phosphorylation, let s first look at the molecules that carry out this complex process. Embedded within the mitochondrial inner membrane are electron transport systems. These are made up of a series of electron carriers, including coenzymes and cytochromes. All these molecules are located within the membrane in an arrangement that allows them to pass electrons from one to the next. This array of electron carriers is called the respiratory electron transport system (Figure 22.7). As you would expect in such sequential oxidation-reduction reactions, the electrons lose some energy with each transfer. Some of this energy is used to make ATP. 

King, F.D. and Packard, T.T., 1975. The effect of hydrostatic pressure on respiratory electron transport system activity in marine zooplankton. Deep-Sea Res., 22 99—105. 

Packard, T.T., Healy, M.L. and Richards, F.A., 1971. Vertical distribution of the activity of the respiratory electron transport system in marine plankton. Limnol. Oceanogr., 16 60—70. 

In closely related species, the primary structures of common proteins are similar. Counting the number of differences in amino acid sequences among these proteins gives some idea of how far various species have diverged in the course of evolution. For example, the protein cytochrome c is an excellent protein for evolutionary comparisons because it is found in the respiratory electron transport system, which is present in all aerobic organisms (Figure 27.8). 

Fig. 4.9. The fatty acid (/3-oxidation) spiral. Fatty acids are degraded to reduced NAD and FAD (flavin adenine dinucleotide) which can transfer electrons to the respiratory electron transport system, and acetyl-CoA which...

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