Oxidative phosphorylation coupling with respiration

In true fermentation, the free energy drop between substrate (say glucose) and anaerobic end products is always modest by comparison with respiration, because fermentation is never based on electron transfer chains coupled to phosphorylation. Rather, true fermentations depend upon a variety of oxidation-reduction reactions involving organic compounds, C02, molecular hydrogen, or sulfur compounds. All these reactions are inefficient in terms of energy yield (moles ATP per mole substrate fermented), and, therefore, the mass of cells obtainable per mole of substrate is much smaller than with respiratory-dependent species. 

Stucki (1980, 1984) applied the linear nonequilibrium thermodynamics theory to oxidative phosphorylation within the practical range of phosphate potentials. The nonvanishing cross-phenomenological coefficients Ly(i v /) reflect the coupling effect. This approach enables one to assess the oxidative phosphorylation with H+pumps as a process driven by respiration by assuming the steady-state transport of ions. A set of representative linear phenomenological relations are given by... 

There is some indications that mitochondria possess a mechanism of self-elimination. This function was ascribed to the so-called permeability transition pore (PTP). The PTP is a rather large nonspecific channel located in the inner mitochondrial membrane. The PTP is permeable for compounds of molecular mass <1.5 kDa. The PTP is usually closed. A current point of view is that PTP opening results from some modification and conformation change of the ATP/ADP antiporter. Oxidation of Cys56 in the antiporter seems to convert it to the PTP in a way that is catalyzed by another mitochondrial protein, cyclophilin. When opened, the PTP makes impossible the performance of the main mitochondrial function, i.e., coupling of respiration with ATP synthesis. This is due to the collapse of the membrane potential and pH gradient across the inner mitochondrial membrane that mediate respiratory phosphorylation. Membrane potential is also a driving force for import of... 

An interesting hypermetabolic myopathy was discovered and biochemically explored by Luft et al. (L7). There was no evidence of hyperthyroidism, and mitochondria from biopsied muscle had a high rate of respiration and a loosely coupled state of oxidative phosphorylation. A few other cases of unusual myopathies with loosely coupled mitochondria have since been described (e.g., S12), although it does not seem that this is a single disease entity. 

Like most bacteria, the Microtox strain has many metabolic pathways which function in respiration, oxidative phosphorylation, osmotic stabilization, and transport of chemicals and nutrients into and out of the cell, and which are located within or near the cytoplasmic membrane. The luciferase pathway [9], which functions as a shunt for electrons directly to oxygen at the level of reduced flavin mono-nucleotide, is also located within the cell membrane complex. This, coupled with lack of membrane-aided compartmentalization of internal functions, gives many target sites at or near the cytoplasmic membrane. These factors all contribute to a rapid response of the organisms to a broad spectrum of toxic substances. 

It is well established that most of the known anaerobic prokaryotes perform oxidative phosphorylation without O2. Depending on the species and the metabolic conditions, these bacteria may use a large variety of inorganic (e.g., nitrate, nitrite, sulfate, thiosulfate, elemental sulfm, polysulfide sulfur) or organic compounds (e.g., fumarate, dimethylsulfoxide, trimethylamine-A -oxide, vinyl- or arylchlorides) as terminal electron acceptor instead of oxygen. The redox reactions with these acceptors are catalyzed by membrane-integrated electron transport chains and are coupled to the generation of an electrochemical proton potential (Ap) across the membrane. Oxidative phosphorylation in the absence of O2 is also termed anaerobic respiration . Oxidative phosphorylation with elemental sulfur is called sulfm respiration . Oxidative phosphorylation with polysulfide sulfur is called polysulfide respiration . 

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