Aerobic dehydrogenases

It is the coenzyme of xanthine oxidase, aldehyde oxidase and other aerobic dehydrogenases. Like riboflavin and FMN, FAD is universally present in the biosphere. It is reddish-yellow in colour but, like FMN and riboflavin, its solutions are a yellow-green. 

Succinate dehydrogenase (Succinate Q oxidore-ductase) Mitochondria and aerobic bacteria Succinate + Q — Fumarate -1- QH2 [PejSJ" [Pe3S,] [Pe,S,T" PAD I-2Cyt b -1-90 to -30 53,54... 

Fig. 3. Protein synthesis in a maize primary root during ( ) one hr pulse labelling with [ HJleucine under aerobic conditions (b)-(e) pulse labelling with [ HJIeucine during the specified times under anaerobic conditions. The arrow labelled TPs indicates the position of the transition polypeptides. The unlabelled arrow indicates the position of alcohol dehydrogenase 1 (ADHl). From Sachs et al. (1980).

The aerobic degradation of several azaarenes involves reduction of the rings at some stage, and are discussed in Chapter 10, Part 1. Illustrative examples include the degradation of pyridines (3-alkyl-pyridine, pyridoxal) and pyrimidines (catalyzed by dihydropyrimidine dehydrogenases). Reductions are involved in both the aerobic and the anaerobic degradation of uracil and orotic acid. 

The carbon monoxide dehydrogenase of the aerobe Oligotropha carboxidovorans contains both Cu and Mo in the form of a cluster in which the Mo is bound to the thiol groups of molybdopterin cytosine nucleotide, and the Cu to cysteine residue in the form of a Cu-S-Mo(=0)OFl cluster (Dobbek et al. 2002). 

This pathway is supported by the demonstration of benzyl alcohol dehydrogenase, benzaldehyde dehydrogenase, benzoyl-CoA ligase, and benzoyl-CoA reductase activities in cell extracts (Biegert and Fuchs 1995). The benzyl alcohol dehydrogenase from benzyl alcohol-grown cells was similar in many of its properties to those from the aerobic bacteria Acinetobacter calcoaceticus and Pseudomonas putida (Biegert et al. 1995). 

Gescher J, W Ismail, E Olgeschlager, W Eisenreich, J Wort, G Fuchs (2006) Aerobic benzoyl-coenzyme A (Co A) catabolic pathway in Azoarcus evansii conversion of ring cleavage product by 3,4-dehydroadipyl-CoA semialdehyde dehydrogenase. J Bacterial 188 2919-2927. 

Mitochondria from body wall muscle and probably the pharynx lack a functional TCA cycle and their novel anaerobic pathways rely on reduced organic acids as terminal electron acceptors, instead of oxygen (Saz, 1971 Ma et al, 1993 Duran et al, 1998). Malate and pyruvate are oxidized intramitochondrially by malic enzyme and the pyruvate dehydrogenase complex, respectively, and excess reducing power in the form of NADH drives Complex II and [3-oxidation in the direction opposite to that observed in aerobic organelles (Kita, 1992 Duran et al, 1993 Ma et al,... 

Fig. 14.1. Role ofthe pyruvate dehydrogenase complex (PDC) during aerobic/ anaerobic transitions in the development of Ascaris suum. PDC, pyruvate dehydrogenase complex AD, acyl CoA dehydrogenase ER, enoyl CoA reductase FR, fumarate reductase SDH, succinate dehydrogenase.

This chapter focuses on the developmental regulation of the pyruvate dehydrogenase complex (PDC). The PDC plays diverse and pivotal roles in the entry of glycolytically generated carbon into the TCA cycle in aerobic stages and the metabolism of mitochondrially generated pyruvate in anaerobic stages (Fig. 14.1). 

Huang, YJ., Walker, D., Chen, W., Klingbeil, M. and Komuniecki, R. (1998b) Expression of pyruvate dehydrogenase isoforms during the aerobic/anaerobic transition in the development of the parasitic nematode, Ascaris suum altered stoichiometry of phosphorylation/inactivation. Archives of Biochemistry and Biophysics 352, 263-270. 

Kuramochi, T., Hirawake, H., Kojima, S., Takamiya, S., Furashima, R., Aoki, T., Komuniecki, R.W. and Kita, K. (1994) Sequence comparison between the flavoprotein subunit of the fumarate reductase (complex II) of the anaerobic parasitic nematode, Ascaris suum, and the succinate dehydrogenase of the aerobic, free-living nematode, Caenorhabditis elegans. Molecular and Biochemical Parasitolog 68, 177-187. 

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