Anaerobic mitochondria

Duran, E., Komuniecki, R.W., Komuniecki, P.R., Wheelock, M.J., Klingbeil, M.M., Ma, Y.C. and Johnson, K.R. (1993) Characterization of cDNA clones for the 2-methyl branched-chain enoyl-CoA reductase. An enzyme involved in branched-chain fatty acid synthesis in anaerobic mitochondria of the parasitic nematode Ascaris suum. Journal of Biological Chemistry 268, 22391—22396. 

Ma, Y.C., Funk, M., Dunham, W.R. and Komuniecki, R. (1993) Purification and characterization of electron-transfer flavoprotein rhodoquinone oxidoreduc-tase from anaerobic mitochondria of anaerobic mitochondria of the adult parasitic nematode, Ascaris suum. Journal of Biological Chemistry 268, 20360-20365. 

Tielens AGM, van Hellemond JJ (2007) Anaerobic mitochondria Properties and origins. In Martin W, Muller M (eds) Origin of Mitochondria and Hydrogenosomes. Springer, Berlin Heidelberg New York, pp 85-104... 

The presence of enzymes with similar function has been recognized in anaerobic mitochondria of kinetoplastid protists and helminths (Tielens et al. 

In this chapter we attempt to complete the list of known eukaryotic taxa that harbour anaerobic mitochondria-like organelles by introducing those... 

Table 1 Taxa containing anaerobic mitochondria-like organelles (MLOs) with the brief summary of the information on MLOs and reference to a figure or original literature. EM - electron microscopy... 

Chance and others also measured the rates at which the different electron carriers became oxidized, following addition of 02 to anaerobic mitochondria, or became reduced after addition of a suitable substrate. When 02 was added, cytochrome a3 became oxidized first, followed by cytochrome a, the c cytochromes, the b cytochromes, and flavins, in that order. Later work showed that UQ became oxidized at about the same rate as the b cytochromes. Observations of this sort led to the proposal that the electron carriers are arranged in the following sequence ... 

Compared with typical aerobic mitochondria, the three main distinctions of these anaerobic mitochondria are (i) the enzyme catalyzing the conversion of fumarate to succinate (ii) the quinone that connects this electron transfer to the enzyme complex in the electron-transport chain and (iii) the presence of ASCT, which converts acetyl-CoA into acetate. These characteristic features of anaerobically functioning... 

Organisms with anaerobic mitochondria can be divided into two different types those which perform anaerobic respiration and use an alternative electron acceptor present in the environment, such as nitrate or nitrite, and those which perform fermentation reactions using an endogenously produced, organic electron acceptor, such as fumarate (Martin et al. 2001 Tielens et al. 2002). An example of the first type is the nitrate respiration that occurs in several ciliates (Finlay et al. 1983), and fungi (Kobayashi et al. 1996 Takaya et al. 2003), which use nitrate and/or nitrite as the terminal electron acceptor of their mitochondrial electron-transport chain, producing nitrous oxide as... 

Fig. 5.2. Possible metabolic pathways in facultative anaerobic mitochondria. Shaded boxes show components of the electron-transport chain used during hypoxia, open boxes are components used during aerobiosis, and the hatched boxes (complex I and ATP-synthase) are components used under aerobic as well as anaerobic conditions. ASCT acetate succinate CoA-transferase, C cytochrome c, Cl, CIII and CIV complexes I, III and IV of the respiratory chain, CITR citrate, ECR enoyl-CoA reductase (such as present in Ascaris suum), ETF electron-transfer flavoprotein, ETF RQ OR electron-transfer flavoproteimrhodoquinone oxidoreductase, FRD fumarate reductase, FUM fumarate, MAE malate, OXAC oxaloacetate, PYR pyruvate, RQ rhodoquinone, SDH succinate dehydrogenase, SUCC succinate, Succ-CoA succinyl-CoA, TER trans-2-enoyl-CoA reductase (such as present in E. gracilis), UQ ubiquinone...

Next to fumarate reduction, some organisms use specific reactions in lipid biosynthesis as an electron sink to maintain redox balance in anaerobically functioning mitochondria. In anaerobic mitochondria two variants are known the production of branched-chain fatty acids and the production of wax esters. The parasitic nematode Ascaris suum reduces fumarate in its anaerobic mitochondria, but instead of only producing acetate and succinate or propionate, like most other parasitic helminths, this organism also use the intermediates acetyl-CoA and propionyl-CoA to form branched-chain fatty acids (Komuniecki et al. 1989). This pathway is similar to reversal of P-oxidation and a complex mixture of the end products acetate, propionate, succinate and branched-chain fatty acids is excreted. In this pathway, the... 

Fig. 5.3. The major components involved in mitochondrial NADH oxidation in facultative anaerobic mitochondria. In anaerobically functioning mitochondria, NADH is oxidized either by soluble enzymes (left) or by membrane-bound complexes of the electron-transport chain (middle). Under aerobic conditions, a classic respiratory chain is used to oxidize NADH (right). Proton translocation is indicated by H with arrows. Ovals represent the electron transporters RQ, UQ and cytochrome c (cyt. c), and electron transport is indicated by dashed arrows. The vertical bar represents a scale for the standard redox potentials in millivolts. Fum fumarate, NADH-DH NADH dehydrogenase, NADH-ECR soluble NADH enoyl-CoA reductase, RQH2 rhodoquinol, Succ succinate, UQH2 ubiquinol...

Adaptations in Electron-Transport Chains in Anaerobic Mitochondria... 

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