Studies on the electron transfer system. 29. The isolation and properties of a succinic dehydrogenase-cytochrome b complex from beef-heart mitochondria

Adiponectin enhances the bioenergetics of cardiac myocytes via an AMPK- and succinate dehydrogenase-dependent mechanism

Adiponectin is one of the most abundant circulating hormones, which through adenosine monophosphate-activated protein kinase (AMPK), enhances fatty acid and glucose oxidation, and exerts a cardioprotective effect. However, its effects on cellular bioenergetics have not been explored. We have previously reported that 5-aminoimidazole-4-carboxamide 1-β-D-ribofuranoside (AICAR, an AMPK activator) enhances mitochondrial respiration through a succinate dehydrogenase (SDH or complex II)-dependent mechanism in cardiac myocytes, leading us to predict that Adiponectin would exert a similar effect via activating AMPK. Our results show that Adiponectin enhances basal mitochondrial oxygen consumption rate (OCR), ATP production, and spare respiratory capacity (SRC), which were all abolished by the knockdown of AMPKγ1, inhibition of SDH complex assembly, via the knockdown of the SDH assembly factor 1 (Sdhaf1), or inhibition of SDH activity. Additionally, Adiponectin alleviated hypoxia-induced reductions in OCR and ATP production, in a Sdhaf1-dependent manner, whereas overexpression of Sdhaf1 confirmed its sufficiency for mediating these effects. Importantly, the levels of holoenzyme SDH under the various conditions correlated with OCR. We also show that the effects of Adiponectin, AMPK, Sdhaf1, as well as, SDH complex assembly all required sirtuin 3 (Sirt3). In conclusion, Adiponectin potentiates mitochondrial bioenergetics via promoting SDH complex assembly in an AMPK-, Sdhaf1-, and Sirt3-dependent fashion in cardiac myocytes.

Human Mitochondrial Pathologies of the Respiratory Chain and ATP Synthase: Contributions from Studies of Saccharomyces cerevisiae

The ease with which the unicellular yeast Saccharomyces cerevisiae can be manipulated genetically and biochemically has established this organism as a good model for the study of human mitochondrial diseases. The combined use of biochemical and molecular genetic tools has been instrumental in elucidating the functions of numerous yeast nuclear gene products with human homologs that affect a large number of metabolic and biological processes, including those housed in mitochondria. These include structural and catalytic subunits of enzymes and protein factors that impinge on the biogenesis of the respiratory chain. This article will review what is currently known about the genetics and clinical phenotypes of mitochondrial diseases of the respiratory chain and ATP synthase, with special emphasis on the contribution of information gained from pet mutants with mutations in nuclear genes that impair mitochondrial respiration. Our intent is to provide the yeast mitochondrial specialist with basic knowledge of human mitochondrial pathologies and the human specialist with information on how genes that directly and indirectly affect respiration were identified and characterized in yeast.

NAPHTHOQUINONE INTERMEDIATE IN THE RESPIRATION OF BACILLUS STEAROTHERMOPHILUS

Downey, R. J. (U.S. Department of Agriculture, Washington, D.C.). Naphthoquinone intermediate in the respiration of Bacillus stearothermophilus. J. Bacteriol. 84:953-960. 1962.-A vitamin K-like naphthoquinone has been isolated from Bacillus stearothermophilus. The compound was susceptible to light (360 mmu) and can be extracted from electron-transport particles with organic solvents. The reduced diphosphopyridine nucleotide (DPNH) oxidase and DPNH-cytochrome c reductase activities in such particles were restored to original levels by the addition of the extracted intermediate, by vitamin K(1), or by menadione. Phosphorylation coupled to the oxidation of malate was restored by addition of the isolated naphthoquinone. Discrepancies in the rate of succinate oxidase and succinate-naphthoquinone reductase activities suggested the intermediate functions in a collateral pathway in the succinate oxidase system of this organism. Anaerobic and aerobic cultivation of the microorganism produced no detectible differences in the character of the intermediate. Reduction of nitrate by the thermophile was not completely dependent upon the naphthoquinone but was significantly stimulated in its presence. No evidence was obtained for the existence of a mixed quinone system in the bacillus.

Preparation and some properties of L-3-glycerophosphate dehydrogenase from pig brain mitochondria

1. A method is described for extraction and partial purification of mitochondrial l-3-glycerophosphate dehydrogenase from pig brain. 2. By the criteria that have so far been applied, the extraction and purification procedures do not modify the activity of the enzyme towards artificial electron acceptors. 3. The amounts of acid-liberatable flavine and iron in the preparation were measured. 4. A study was made of the effects of various analogues of l-3-glycerophosphate on the activity of the enzyme.