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Health, Safety & Environment

Ethylbenzene dehydrogenase

The first step in anaerobic ethylbenzene mineralization in denitrifying Azoarcus so. strain EB1 is the oxidation of ethylbenzene to (S)-(-)-1-phenylethanol. Ethylbenzene dehydrogenase, which catalyzes this reaction, is a unique enzyme in that it mediates the stereoselective hydroxylation of an aromatic hydrocarbon in the absence of molecular oxygen. Purified ethylbenzene dehydrogenase contains approximately 0.5 mol of molybdenum, 16 mol of iron, and 15 mol of acid-labile sulfur per mol of holoenzyme, and a molydopterin cofactor. According to sequence analysis and biochemical data ethylbenzene dehydrogenase is a novel member of the dimethyl sulfoxide reductase family of molybdopterin-containing enzymes.

Johnson, H.A., Pelletier, D. A., and Spormann, A. M., Isolation and characterization of anaerobic ethylbenzene dehydrogenase, a novel Mo-Fe-S enzyme, Journal of Bacteriology, 2001, 183, 4536-4542.

 

Characterisation of the redox centers of ethylbenzene dehydrogenase

Ethylbenzene dehydrogenase (EbDH, the initial enzyme of anaerobic ethylbenzene degradation from the beta-proteobacterium Aromatoleum aromaticum, is a soluble periplasmic molybdenum enzyme consisting of three subunits. It contains a Mo-bis-molybdopterin guanine dinucleotide (Mo-bis-MGD cofactor and an 4Fe-4S cluster (FS0 in the α-subunit, three 4Fe-4S clusters (FS1 to FS3 and a 3Fe-4S cluster (FS4 in the β-subunit and a heme b cofactor in the γ-subunit. Ethylbenzene is hydroxylated by a water molecule in an oxygen-independent manner at the Mo-bis-MGD cofactor, which is reduced from the Mo(VI to the Mo(IV state in two subsequent one-electron steps. The electrons are then transferred via the Fe-S clusters to the heme b cofactor. In this report, we determine the midpoint redox potentials of the Mo-bis-MGD cofactor and FS1-FS4 by EPR spectroscopy, and that of the heme b cofactor by electrochemically induced redox difference spectroscopy. We obtained relatively high values of > 250 mV both for the Mo(VI-Mo(V redox couple and the heme b cofactor, whereas FS2 is only reduced at a very low redox potential, causing magnetic coupling with the neighboring FS1 and FS3. We compare the results with the data on related enzymes and interpret their significance for the function of EbDH.

C. Hagel, B. Blaum, T. Friedrich, and J. Heider,Characterisation of the redox centers of ethylbenzene dehydrogenase, J Biol Inorg Chem, 2022, 27, 143-154.

             

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