Uncouplers detergents

Respiring mitochondria extrude protons. A weakly buffered suspension of mitochondria is provided with an oxidizable substrate and allowed to use up all the O2 in the solution. The traces show measurements of the pH of the suspension, with pH decreases plotted upward. When a small amount of O2 is added (upward-pointing arrow), respiration can occur for a few seconds. The pH of the solution decreases suddenly at this point (Exp. A). The pH change persists for a period of several minutes, long after the 02 has been used up. If an uncoupler is added, the pH returns abruptly to nearly its original level. Experiment B was done in the presence of a detergent that disrupted the inner membrane, making the membrane... 

Potentiometric reductive titration, using both fresh thylakoids and PS II particles previously oxidized with ferricyanide, has revealed that the LP couple exhibits a constant midpoint redox potential ( o- +° 12 v ) above pH 7.6, but becomes pH-dependent below this pH, with a slope of about -60 mV pH pH unit, whereas the HP couple is pH-independent in the pH range between 6.5 an 8.5 ( o-+0 36 V) in general, cytochrome b-559 exhibits potential values about 40 mV lower in thylakoids than in PS II particles. After mild heating of the fresh preparations or treatment with the detergent Triton X-100, the HP couple is converted into the LP couple, which preserves its characteristic pH-dependence. In contrast, in the presence of the uncoupler CCCP, the HP couple is also converted into the LP couple, but the pH-dependence proper to the latter is now lost. 

It has been criticized that the effect of acyl-CoA is unspecific and due to a general detergent action. However, acyl-CoA does not induce permeability in parallel with Cl permeability [85], and there are clearly effects of palmitoyl-CoA on brown fat mitochondria at concentrations below those that yield (definitely unspecific ) uncoupling in rat liver mitochondria. Further, the uncoupling effects of free fatty acids are clearly — at low concentrations — better if acyl-CoA formation is allowed to proceed than when it is hampered [81] (Fig. 10.14). 

Lobareva et al. [228] provided evidence that B. brevis excretes over 90% of its GS which is then bound to the outside of the spores. The bound GS can be removed (with difficulty) by water or buffer, the ease of which is dependent on the presence or absence of detergents and also pH. They showed that it is not merely a case of insoluble GS in suspension but that soluble GS binds to the cells. They believe this excretion process is the way B. brevis protects itself against GS uncoupling of electron transport and phosphorylation, i. e., energy production. 

Special considerations for membrane protein expression in E. coli include issues of targeting ideally the expressed protein can be incorporated into the bacterial cell membrane, allowing extraction of folded samples from detergent-solubilized cell membranes [34—37]. This has been the case for the small number of polytopic helical membrane protein structures that were successfully determined by solution NMR, namely diacylglycerol kinase (DAGK) [38], the disulfide bond isomerase DsbB [39], sensory rhodopsin II (pSRII) [40], and the mitochondrial uncoupling... 

Brustovetskii NN, Dedukhova VN, Egorova MV, Mokhova EN, Skulachev VP. Uncoupling of oxidative phosphorylation by fatty acids and detergents suppressed by ATP/ADP antiporter inhibitors. Biochem (Moscow) 1991 56 1042-1048. 

Various chemicals cause uncoupling by increasing the permeability of the membrane to protons and other small ions. Detergents, which destabilize the membrane structure, can have this effect [15]. Several small molecules, including some classical uncouplers, have been described as affecting the membrane permeability transition (MPT), which causes a dramatic increase in the ability of ions to move across the membrane [9, 16, 17]. More specific effects that increase the permeability of the membrane to protons, as caused by the peptide gramicidin A, also lead to uncoupling [14, 18, 19]. 

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