Around 30–40 years after the first isolation of the five complexes of oxidative phosphorylation from mammalian mitochondria, we present data that fundamentally change the paradigm of how the yeast and mammalian system of oxidative phosphorylation is organized. The complexes are not randomly distributed within the inner mitochondrial membrane, but assemble into supramolecular structures. We show that all cytochrome c oxidase (complex IV) of Saccharomyces cerevisiae is bound to cytochrome c reductase (complex III), which exists in three forms: the free dimer, and two supercomplexes comprising an additional one or two complex IV monomers. The distribution between these forms varies with growth conditions. In mammalian mitochondria, almost all complex I is assembled into supercomplexes comprising complexes I and III and up to four copies of complex IV, which guided us to present a model for a network of respiratory chain complexes: a ‘respirasome’. A fraction of total bovine ATP synthase (complex V) was isolated in dimeric form, suggesting that a dimeric state is not limited to S.cerevisiae , but also exists in mammalian mitochondria.

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Supercomplexes in the respiratory chains of yeast and mammalian mitochondria

The Ratio of Oxidative Phosphorylation Complexes I–V in Bovine Heart Mitochondria and the Composition of Respiratory Chain Supercomplexes

Respiratory chain supercomplexes of mitochondria and bacteria.

1. The occurrence and relative abundance of adipose tissue around the heart and in the pericardium of wild and domesticated mammals are reviewed and some new data reported. 2. For macaque monkeys and a wide range of other adult mammals, the mean volume of epicardial adipocytes is constant at about half the average of that of other depots, although the relative mass of this depot is unrelated to the abundance of adipose tissue in the rest of the body. 3. In young adult guinea-pigs, the maximum rate of fatty acid synthesis is significantly higher in epicardial adipose tissue than that in the pericardial, perirenal and popliteal depots. 4. The rate of fatty acid release by epicardial adipose tissue is approximately twice that of the pericardial and perirenal depots. 5. The protein contents of guinea-pig epicardial and pericardial adipose tissue are similar, and are significantly higher than those of the perirenal and popliteal adipose tissue and there are no site-specific differences in the abundance of mitochondria. 6. In adult Macaca monkeys, the capacity of the epicardial adipose tissue for glucose utilization is about half that of the intra-abdominal depots. 7. The principal difference between epicardial adipose tissue and that elsewhere in the body is its greater capacity for fatty acid release. 8. It is suggested that cardiac adipose tissue may act as a local energy supply for adjacent myocardium and/or as a buffer against toxic levels of free fatty acids.

Adipose tissue in the mammalian heart and pericardium: structure, foetal development and biochemical properties

SPECIFIC AIMTo assess whether the antioxidant properties of melatonin are suitable to maintain GSH homeostasis counteracting mitochondrial oxidative stress.PRINCIPAL FINDINGS1. Effect of melatonin, NAC, ascorbate, and Trolox on mitochondrial GSH and GSSG levelsIn basal conditions, i.e., mitochondria incubated in the absence of t-BHP, melatonin (100 nM) significantly (P<0.001) increased the content of GSH and decreased that of GSSG in brain (GSH: 6.82±0.78 to 10.13±0.42 nmol/mg prot) and liver (GSH: 11.54±0.89 to 19.43±0.80 nmol/mg prot; GSSG: 1.44±0.22 to 0.06±0.007 nmol/mg prot) mitochondria. The other antioxidants tested were unable to exert a similar effect of melatonin, and only the dose of 1000 μM Trolox increased GSH levels (11.50 ± 0.43 nmol/mg prot) in brain mitochondria.After incubation with 100 μM t-BHP, practically all GSH was oxidized to GSSG (Fig. 1)⤻ . Melatonin (100 nM) counteracted these toxic effects, recovering the basal levels of GSH and GSSG. In this situation, i.e., t-BHP-induced oxid...

Melatonin but not vitamins C and E maintains glutathione homeostasis in t-butyl hydroperoxide-induced mitochondrial oxidative stress.

Publisher Summary This chapter describes the preparation and properties of succinie–cytochrome c reductase (complex II - III). Assays of enzymatic activity are carried out at 38° in a Beckman Model DU spectrophotometer, equipped with a photomultiplier. The final reaction mixture contains ten micromoles phosphate buffer (0.10 ml); one micromole NaN3 (0.01 ml); 0.2 micromole EDTA (0.02 ml); five mg BSA (0.05 ml); 10 micromoles potassium succinate, pH 7.0 (0.10 ml); and water to a volume of 0.9 ml. The enzyme preparation to be assayed is diluted to a concentration of 100-200 μg protein per milliliter in a solution of 0.88 M sucrose 0.005 M in succinatc. The enzyme-catalyzed reduction of cytochrome c by succinate proceeds at a linear rate under standard conditions over the first minute. Then specific activity is calculated. The resulting increase in absorbancy at 550 mμ is followed during this linear phase. In the method of preparation as described in the chapter, beef heart mitochondria are isolated in 0.25 M sucrose and are frozen at –40° for a period of 1-7 days. The yield and increase of activity during the purification of the succinic-cytochrome c reductase is also illustrated.

Howard D. Tisdale

Papers

[39] Preparation and properties of succinic—cytochrome c reductase (complex II–III)