Electron transfer, and respiration

Eugene Kennedy and Albert Lehninger showed in 1948 that, in eulcaiyotes, the entire set of reactions of the citric acid cycle takes place in mitochondria. Isolated mitochondria were found to contain not only all the enzymes and coenzymes required for the citric acid cycle, but also all the enzymes and proteins necessaiy for the last stage of respiration—electron transfer and ATP synthesis by oxidative phosphoiylation. As we shall see in later chapters, mitochondria also contain the enzymes for the oxidation of fatty acids and some amino acids to acetyl-CoA, and the oxidative degradation of other amino acids to a-ketoglutarate, succinyl-CoA, or oxaloacetate. Thus, in nonphotosynthetic eulcaiyotes, the mitochondrion is the site of most energy-yielding... 

FIGURE 19-18 Coupling of electron transfer and ATP synthesis in mitochondria. In experiments to demonstrate coupling, mitochondria are suspended in a buffered medium and an 02 electrode monitors 02 consumption. At intervals, samples are removed and assayed for the presence of ATP. (a) Addition of ADP and P, alone results in little or no increase in either respiration (02 consumption black) or ATP synthesis (red). When succinate is added, respiration begins immediately and... 

Halocyanins have been isolated from a haloalkaliphillic archaebacterium." They may be involved in electron transfer in respiration chains that include cytochrome be and a terminal oxidase cytochrome Uclacyanins have been isolated from Arabidopsis plant." They have... 

Therefore, G. sulfurreducens biofilm electron transfer is generally described as complete acetate oxidation to carbon dioxide, protons, and electrons in which electron transfer outside the cells is the rate-limiting step. The mass transfer of protons and carbon dioxide affects pH buffering and has been shown to affect the biofilm. Throughout the rest of this chapter, we consider only electron transfer and pH effects, ignoring changes in metabolic activity of the biofilm. Only the metabolic respiration rate, approximated by the current measured at the biofilm electrode, is considered. This does not mean that changes in metabolic activity are less important. We refer the readers to Chapter 2 for more information on G. sulfurreducens metabolism. 

In Figure 5.11, we described the interplay between electron transfer and mass transfer and how both are required to observe a current from a G. sulfurreducens biofilm. It is difficult to determine the role of mass transfer in biofilms simply from cyclic voltammograms usually, certain electrochemical setups are required to investigate mass transfer via electrochemical methods. In our case, we used a combination of EIS and RDEs to study electron transfer and diffusional processes in G. sulfurreducens biofilms respiring on electrodes [50]. We tested the hypothesis that the RDE can be used as an electrochemical tool that controls diffusional processes when EABs are studied. We determined the film resistance, film capacitance, interfacial resistance, interfacial capacitance, and pseudocapacitance of G. sulfurreducens biofilms as shown in Eigure 5.23. The details of the calculations and experimental procedures are given in the literature [50],... 

Fig. 6. Diagram representing the relation between the luminescent system of bacteria and the general pathway of hydrogen or electron transfer in respiration (10,126). The drawing is not to scale.

Ramirez B E, Malmstrom B G, Winkler J R and Gray H B 1995 The currents of life the terminal electron-transfer complex of respiration Proc. Natl Acad. Sc/., USA 92 11 949-51... 

The many redox reactions that take place within a cell make use of metalloproteins with a wide range of electron transfer potentials. To name just a few of their functions, these proteins play key roles in respiration, photosynthesis, and nitrogen fixation. Some of them simply shuttle electrons to or from enzymes that require electron transfer as part of their catalytic activity. In many other cases, a complex enzyme may incorporate its own electron transfer centers. There are three general categories of transition metal redox centers cytochromes, blue copper proteins, and iron-sulfur proteins. 

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