A role for fatty acid peroxy radicals in the cyanide-insensitive pathway of plant mitochondria?

Cyanide resistant respiration and the alternative oxidase pathway: A journey from plants to mammals

In a large number of organisms covering all phyla, the mitochondrial respiratory chain harbors, in addition to the conventional elements, auxiliary proteins that confer adaptive metabolic plasticity. The alternative oxidase (AOX) represents one of the most studied auxiliary proteins, initially identified in plants. In contrast to the standard respiratory chain, the AOX mediates a thermogenic cyanide-resistant respiration; a phenomenon that has been of great interest for over 2 centuries in that energy is not conserved when electrons flow through it. Here we summarize centuries of studies starting from the early observations of thermogenicity in plants and the identification of cyanide resistant respiration, to the fascinating discovery of the AOX and its current applications in animals under normal and pathological conditions.

Induction of petite mutation with acriflavine and elevated temperature in Candida albicans

A method of inducing respiratory deficient (petite) mutation in Candida albicans (which has been previously classed as a petite-negative yeast) and characteristics of some isolated mutants are reported. When grown at 42 degrees C in the presence of a cytoplasmic mutagen (acriflavine), C. albicans exhibited diauxie-like biphasic growth. Mutants which were unable to grow on a non-fermentable substrate, glycerol, were isolated from the above culture at a frequency of less than 1%. The simultaneous action of both acriflavine and a supraoptimal temperature of 42 degrees C was required to induce respiratory mutation. The respiratory mutants were separated into two groups: i. mutants exhibiting a complete cytochrome spectrum but with low respiratory activity and ii. those deficient in cytochrome aa3. Further characterization of their respiratory activity, colony morphology, mitochondrial morphology and growth manner supported the evidence that members of the latter group can be regarded as petite mutants.

Discrimination between duroquinol oxidase activity and the terminal oxidation step of the cyanide-resistant electron transport pathway of plant mitochondria

Comparison of the cyanide-resistant duroquinol oxidase activity of sub-mitochondrial particles from Arum maculatum L. with their ability to carry out a cyanide-resistant oxidation of NADH and succinate shows that heat-inactivation of the duroquinol oxidase activity does not proportionally affect NADH and succinate oxidation. Moreover, 1 microM antimycin inhibits duroquinol oxidase activity by 50% while not decreasing the rates of NADH and succinate oxidation. Therefore, the cyanide-resistant electron transport does not appear to be mediated by a "duroquinol oxidase", and a convincing proof of the existence of a specific protein acting as a cyanide-resistant oxidase in plant mitochondria is still lacking.

A study of cyanide-insensitive respiration in the genus Dekkera and Brettanomyces

Dekkera intermedia and Brettanomyces custersii were shown to have a respiratory pathway resistant to cyanide, antimycin A, and azide. This respiration remained sensitive to salicylhydroxamic acid (SHAM). The "cyanide-resistant" respiration was induced mainly at the end of the growth phase and could reach 50% of total respiratory capacity. The mitochondrial "petite colony" mutation had no effect on this oxidation pathway. The presence of this respiration pathway in these strains constitutes a compensation mechanism for the reducing activity of acetaldehyde dehydrogenase. This alternate pathway would thus be a fundamental element of the Custer effect, a characteristic feature of these strains.

Oxidation of cysteine to cystine by membrane fractions of Chlorella fusca

Isolated membrane fractions of Chlorella fusca 211-8b obtained by french-press treatment and sonication catalyzed the oxidation of L-cysteine to L-cystine. The pH-optimum of this reaction was determined to be around 8-8.5 and a stoichiometry of 4 SH-groups oxidized for one O2 consumed was obtained. This thiol-oxidation system was specific for D-and L-cysteine; DL-homocysteine and cysteamine were oxidized at about half the rate whereas all other thiols tested including glutathione, mercaptoethanol, mercaptopropionic acid and dithioerythritol were not oxidized by these membrane fractions. The apparent Km for L-cysteine was determined as 3.3 mmol l(-1). Rates of 200 μmol cysteine oxidized mg(-1) chlorophyll h(-1) were normally obtained. Extremely high rates of oxygen uptake were measured using L-cysteine methyl ester and L-cysteine ethyl ester. This thioloxidation system was not inhibited by mitochondrial electron-transport inhibitors such as rotenone or antimycin A, nor by the chloroplast electron-transport inhibitors 2,5-dibromothymochinone and 2,4-dinitrophenylether of iodonitrothymol. The cysteine oxidation catalyzed by C. fusca membranes was inhibited, however, by salicylhydroxamic acid, o-phenanthrolin, N,N'-disalicyliden-1,3-diaminopropane 5,5'-disulfonic acid, ethylenediaminetetraacetic acid, high KCN levels and by the buffers, N-[2-hydroxyl-1,1-bis(hydroxymethyl) ethyl] glycine and phosphate. This cysteine-oxidation system seems to function as a counterpart of thioredoxin-mediated light activation of enzymes, allowing reduced thiol groups to be oxidized again by O2 (dark inactivation).