Respiration pathways

In the absence of 02 the E. coli FNR protein induces proteins of the anaerobic respiration pathways. Nitrate also has its own two-component system that senses nitrate availability and activates transcription of enzymes catalyzing nitrate respiration.162 An expanded two-component system induces sporulation in Bacillus subtilis in response to poor growth conditions.163164 The crystal structure of one of two response regulators (SpoOF) has a structure closely related to that of CheY and the nitrate response regulator NarL. 

In the heart and brain, the experimental value of q for the cellular respiration pathway is close to the value of f/,cc = 0.953, which suggests that the pathway is optimized to economical ATP for cellular processes. In the brain, the coupling of the acetic acid cycle approaches qv = 0.91, suggesting a maximized cellular energy state. However, in the heart, the acetic acid cycle coupling is 0.786, which is between qp and e/r, and consistent with the maximum ATP production necessary for preserving the cellular energy state (Stucki, 1980 Cairns et al., 1998). 

Figure 2 The eumulative fraction of carbon burial and the respiration pathways as a function of depth in the oeean derived from the global diagenesis model of Archer et al. (2002) (after Archer et aL, 2002).

Oxireductases Dehydrogenases Oxidases Reductases Oxygenases Peroxidases Catalases Catalyze oxidation-reduction reactions. Important in fermentation and respiration pathways. 

Fig. 2.2.1. Respirative pathways which are related to CO2 exchange and carbonate precipitation by bacteria and algae.

Depending on the state of the cell, either reductive (fermentation) or oxidative (respiration) pathways are active, yielding different final products. 

In addition to the reduction potentials of different terminal electron acceptors utilized in the anaerobic ETC, presence of other compounds has also found to be essential for the efficiency of anaerobic respiration. One important factor is metal ion homeostasis. This is because many enzymes in the anaerobic respiratory pathways are metal containing enzymes. It was reported that expression of operons containing enzymes in the anaerobic respiration pathway is highly reduced upon iron limitation under anaerobic conditions while the aerobic respiration pathways are only modestly affected in E. coli (Cotter et al. 1992). Moreover, induction of DMSO respiration pathways is reported to be dependent on the molybdate uptake (McNichoIas et al. 1998). 

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