Structural studies of methylamine dehydrogenase

Abstract

Methylamine dehydrogenase (MADH), found in methyldtrophic bacteria, is an inducible, periplasmic quinoenzyme which catalyzes the oxidation of methylamine to formaldehyde and ammonia (De Beer R et al. 1980). It contains the novel cofactor tryptophan tryptophylquinone (TTQ), which is derived from two tryptophan side chains (McIntire WS et al. 1991). Subsequently, electrons are transferred to the membrane bound terminal oxidase, cytochrome aa₃ via a series of soluble electron carrier proteins. In facultative autotrophs, such as Paracoccus denitrificans, the initial electron acceptor in this chain is amicyanin, a blue copper protein (Husain M, Davidson VL 1985), while in Methylophilus methylotrophus W3A1, which lacks the gene for amicyanin (Chistoserdov AY et al. 1994) the initial acceptor is a cytochrome c₅₅₂ (Chandrasekar R Clapper MH 1986). In the case of P. denitrificans, in vitro studies suggest that the acceptor following amicyanin in the electron transfer chain is cytochrome c_551i(Husain M, Davidson VL 1986). All three proteins are induced when these bacteria are grown on methylamine as the sole carbon source.