ABSTRACT
Methylotrophic bacteria contain several unusual dehydrogenases which oxidize methyl groups to formaldehyde as a first step in the utilization of methanol and methylated amines. Trimethylamine dehydrogenase is an iron-sulfur flavoprotein comprised of two identical subunits, each of which contains an cluster and covalently bound flavin in the unusual form of 6-S-cysteinyl-flavin mononucleotide. A number of favorable properties, notably its inherent stability and abundance, has contributed to make trimethylamine dehydrogenase one of the best characterized iron-sulfur flavoproteins. In the majority of methylotrophs capable of growth on trimethylamine as carbon source, trimethylamine is converted to trimethylamine-/V-oxide by a trimethylamine monooxygenase and subsequently to formaldehyde and dimethylamine by a trimethylamine-A'-oxide de-methylase. Dimethylamine, the product of oxidative demethylation of trimethylamine, was found to reduce trimethylamine dehydrogenase slowly. In agreement with the slower intramolecular electron transfer at high substrate concentrations, trimethylamine dehydrogenase from both sources showed partial substrate inhibition.
