Uncoupling of mitochondrial oxidative phosphorylation by thallium.

The mechanism of integration of λ$\text{bio}$ll, which is deleted of all the known λ recombination genes, was studied using $\text{bio}$ deleted hosts as recipients. The presence of $\text{rec}$BC DNase and $\text{exo}$I in the recipient cells affected the fate of λ$\text{bio}$ll DNA. In nine of ten $\text{imm}\text{λ}{}^{\mathrm{+}}$ transductants, insertion of the λ$\text{bio}$ll genome took place somewhere between J and N and the remaining one had abnormally permuted prophage λ. In this lysogen (#42), the sequence of prophage genes was similar to that of vegetative phage λ. The properties of lysogen #42 were compared with those of other lysogens.     

Uncoupling effect of fungal hydroxyanthraquinones on mitochondrial oxidative phosphorylation

Structure-uncoupling activity relationship of seven anthraquinone derivatives were investigated using rat liver mitochondria. Three compounds bearing the free hydroxyl group at the beta-position of their anthraquinone nucleus (1,3,6,8-tetrahydroxyanthraquinone, 1-acetyl-2,4,5,7-tetrahydroxy-9,10-anthracenedione and skyrin) exhibited uncoupling effect. Rugulosin, rugulin and physcion (all lacking the hydroxyl at the beta-position) were ineffective. Erythroglaucin, a derivative of physcion with the free hydroxyl group at the gamma-position, exhibited the highest uncoupling activity in the series tested. In addition, erythroglaucin abolished the energy dependent Ca2+ retention in mitochondria and induced Ca2+ leak. It also prevented the energization of mitochondrial membrane by ATP and induced a loss of the ATP induced membrane potential similarly as did carbonylcyanamide-3-chlorophenyl hydrazone (CCCP). The data show that the free hydroxyl group at either the gamma-position or the beta-position of anthraquinone nucleus is a prerequisite of the uncoupling activity of hydroxyanthraquinones.     

Uncoupling effect of protonophoric and nonprotonophoric analogs of carbonyl cyanide phenylhydrazone on mitochondrial oxidative phosphorylation

Analogs of carbonyl cyanide phenylhydrazone providing no reaction with nucleophilic groups and lacking acidobasic properties, respectively, were synthesized for study of mechanism of uncoupling effect on oxidative phosphorylation. Their retention, influence on proton transport, abilities to SH--groups modify and to stimulate respiration in rat liver mitochondria, together with their physico-chemical properties, namely lipophilicity, acidobasicity and reactivity were characterized. The substitution of acidic hydrogen of the imino group resulted in the loss of both acidobasicity and uncoupling effect on oxidative phosphorylation. A decreased reactivity resulted from the substitutions of nitrile groups with the uncoupling activity remaining preserved.     

Inhibition of mitochondrial oxidative phosphorylation by adriamycin

The antitumour antibiotic, adriamycin, inhibited oxidative phosphorylation in freshly prepared mitochondria from the heart, liver and kidney of the rat. It abolished respiratory control and stimulated ATPase activity. Succinate oxidation by heart mitochondria was extremely sensitive to the drug when hexokinase was present in the reaction medium. The sensitive site has been identified to lie in the region between the succinate dehydrogenase flavoprotein and ubiquinone of the respiratory chain.     

Control of mitochondrial oxidative phosphorylation

The objective of this investigation is to analyze the two following problems of the regulation of mitochondrial oxidative phosphorylation: what is the extramitochondrial parameter that controls ATP production according to the cytoplasmic demands and how the control is distributed between various mitochondrial enzymes. On the basis of the data of Groen et al. (1982) it is shown that as the respiration rates ranged over 30-50% of the maximum (i.e. within the physiological region) the contribution of the adenine nucleotide translocator to the control of the ATP flux is no less than 90%, referring to the total contribution of all mitochondrial enzymes as 100%. Founding on the key role of the adenine nucleotide translocator it has been concluded that besides the extramitochondrial [ATP]/[ADP] ratio the absolute ADP concentration is another extramitochondrial signal controlling significantly the rate of oxidative phosphorylation.     

Uncouplers of rat-liver mitochondrial oxidative phosphorylation

1. The ability of a series of compounds to uncouple oxidative phosphorylation of rat-liver mitochondria has been investigated. 2. The compounds were: 2-amino-1,1,3-tricyanopropene; carbonyl cyanide phenylhydrazone and its m-chloro and p-trifluoromethoxy derivatives; 4,5,6,7-tetrachloro-, 5-chloro-4-nitro-, 5-nitro-and 4,5,6,7-tetrachloro-1-methyl-benzotriazole; 4-hydroxy-3,5-di-iodo-, 3,5-di-bromo-4-hydroxy- and 3,5-dichloro-4-hydroxy-benzonitrile; and pentafluorophenol. 3. In a medium the components and physical condition of which were, as far as possible, kept constant, each compound was tested for ability to stimulate adenosine triphosphatase, to stimulate respiration in the presence of pyruvate as substrate, to inhibit phosphate uptake and to prevent swelling by trimethyltin. 4. Each compound was also examined with respect to its ability to produce rapid rigor mortis in mice. 5. The biological properties were compared with the dissociation constant and the hexane–water partition coefficient for each compound. 6. With the exception of 4,5,6,7-tetrachloro-1-methylbenzotriazole, all the compounds behaved qualitatively as 2,4-dinitrophenol. 7. Within each class of compound there is a relation between biological activity and the physical attributes measured. 8. The most efficient uncouplers were the most acidic and the most hydrophobic.     

Mechanistic stoichiometry of mitochondrial oxidative phosphorylation

P/O ratios of rat liver mitochondria were measured with particular attention to systematic errors. Corrections for energy loss during oxidative phosphorylation were made by measurement of respiration as a function of mitochondrial membrane potential. The corrected values were close to 1, 0.5, and 1 at the three coupling sites, respectively. These values are consistent with recent measurements of mitochondrial proton transport.     

Uncoupling of oxidative phosphorylation by curcumin: Implication of its cellular mechanism of action

Curcumin is a phytochemical isolated from the rhizome of turmeric. Recent reports have shown curcumin to have antioxidant, anti-inflammatory and anti-tumor properties as well as affecting the 5′-AMP activated protein kinase (AMPK), mTOR and STAT-3 signaling pathways. We provide evidence that curcumin acts as an uncoupler. Well-established biochemical techniques were performed on isolated rat liver mitochondria in measuring oxygen consumption, F₀F₁-ATPase activity and ATP biosynthesis. Curcumin displays all the characteristics typical of classical uncouplers like fccP and 2,4-dinitrophenol. In addition, at concentrations higher than 50 μM, curcumin was found to inhibit mitochondrial respiration which is a characteristic feature of inhibitory uncouplers. As a protonophoric uncoupler and as an activator of F₀F₁-ATPase, curcumin causes a decrease in ATP biosynthesis in rat liver mitochondria. The resulting change in ATP:AMP could disrupt the phosphorylation status of the cell; this provides a possible mechanism for its activation of AMPK and its downstream mTOR and STAT-3 signaling.     

Flow-force relationships in mitochondrial oxidative phosphorylation

The rates of oxidation and phosphorylation in isolated rat-liver mitochondria have a steep dependence on the protonmotive force (delta mu H+) across the membrane. These experimentally observed relationships proved to be independent of the way in which delta mu H+ was varied. These results were obtained when the membrane potential (delta psi) was calculated from the distribution of K+ (in the presence of valinomycin). When triphenylmethylphosphonium (TPMP+) was used as a probe for delta psi, slightly different flow-force relationships were obtained. We conclude that unique relationships exist between delta mu H+ and the rates of oxidation and phosphorylation, and that under some conditions the behaviour of the probe TPMP+ is anomalous.