Methylotrophs, trimethylamine dehydrogenase

The properties of the semiquinone from of the ETF isolated from the methylotrophic bacterium resemble those of the bacterial flavodoxins with the exception that flavodoxins form neutral semiquinones whereas this ETF forms an anionic semiquinone. Nearly quantitative anionic semiquinone formation is observed either in the presence of excess dithionite or when excess trimethylamine and a catalytic amount of trimethylamine dehydrogenase are added. Of interest is the apparent stability of the anionic semiquinone towards oxidation by O2 but not to oxidizing agents such as ferricyanide. This appears to be the first example of an air-stable protein-bound anionic flavin semiquinone. Future studies on the factors involved in imparting this resistance to O2 oxidation by the apoprotein are looked forward to with great interest. 

Trimethylamine dehydrogenase is an iron-sulfur flavoprotein found in the methylotrophic bacterium Methylophilus methylotrophus W3A1. It catalyzes the oxidative N-demethylation of trimethylamine by water with formation of dimethylamine and formaldehyde (Steenkamp and Mallinson, 1976). The protein is a symmetrical dimer consisting of 166kDa subunits (Kasprzak et al., 1983 Lim et al., 1982). Each subunit contains one 4Fe-4S center and one FMN cofactor. The latter is bound covalently through the 6... 

Steenkamp, D. J., and Beinert, H., 1982a, Mechanistic studies on the dehydrogenases of methylotrophic bacteria. 1. The influence of substrate binding to reduced trimethylamine dehydrogenase on the intramolecular electron transfer between its prosthetic groups, Biochem. J. 207 2339239. 

Steenkamp, D. J., and Mallinson, J., 1976, Trimethylamine dehydrogenase from a methylotrophic bacterium. I. Isolation and steady-state kinetics, Biochim. Biophys. Acta 429 7059719. 

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