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Mechanism of reaction of allylamine with the quinoprotein methylamine dehydrogenase.

ABSTRACT: Allylamine did not serve as an efficient substrate for methylamine dehydrogenase (EC 1.4.99.3) in a steady-state assay of activity and appeared to act as a competitive inhibitor of methylamine oxidation by methylamine dehydrogenase. Transient kinetic studies, however, revealed that allylamine rapidly reduced the tryptophan tryptophylquinone (TTQ) cofactor of methylamine dehydrogenase. The rate of TTQ reduction by allylamine was 322 s-1, slightly faster than the rate of reduction by methylamine. These data were explained by a kinetic mechanism in which allylamine and methylamine are alternative substrates for methylamine dehydrogenase. The apparent competitive inhibition by allylamine is due to a very slow rate of release of the aldehyde product, 0.28 s-1, relative to a rate of 18.6 s-1 for the release of the aldehyde product of methylamine oxidation. A reaction mechanism is proposed for the oxidative deamination of allylamine by methylamine dehydrogenase. This mechanism is discussed in relation to the reaction mechanisms of topa-bearing quinoprotein amine oxidases, the flavoprotein monoamine oxidase and the mammalian semicarbazide-sensitive amine oxidase.

SUBMITTER: Davidson VL

PROVIDER: S-EPMC1136951 | biostudies-other | 1995 Jun

REPOSITORIES: biostudies-other

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Project description:Methylamine plays an important role in the global carbon and nitrogen budget; microorganisms that grow on reduced single carbon compounds, methylotrophs, serve as a major biological sink for methylamine in aerobic environments. Two non-orthologous, functionally degenerate routes for methylamine oxidation have been studied in methylotrophic Proteobacteria: Methylamine dehydrogenase and the N-methylglutamate pathway. Recent work suggests the N-methylglutamate (NMG) pathway may be more common in nature than the well-studied methylamine dehydrogenase (MaDH, encoded by the mau gene cluster). However, the distribution of these pathways across methylotrophs has never been analyzed. Furthermore, even though horizontal gene transfer (HGT) is commonly invoked as a means to transfer these pathways between strains, the physiological barriers to doing so have not been investigated. We found that the NMG pathway is both more abundant and more universally distributed across methylotrophic Proteobacteria compared to MaDH, which displays a patchy distribution and has clearly been transmitted by HGT even amongst very closely related strains. This trend was especially prominent in well-characterized strains of the Methylobacterium extroquens species, which also display significant phenotypic variability during methylamine growth. Strains like Methylobacterium extorquens PA1 that only encode the NMG pathway grew on methylamine at least five-fold slower than strains like Methylobacterium extorquens AM1 that also possess the mau gene cluster. By mimicking a HGT event through the introduction of the M. extorquens AM1 mau gene cluster into the PA1 genome, the resulting strain instantaneously achieved a 4.5-fold increase in growth rate on methylamine and a 11-fold increase in fitness on methylamine, which even surpassed the fitness of M. extorquens AM1. In contrast, when three replicate populations of wild type M. extorquens PA1 were evolved on methylamine as the sole carbon and energy source for 150 generations neither fitness nor growth rate improved. These results suggest that the NMG pathway permits slow growth on methylamine and is widely distributed in methylotrophs; however, rapid growth on methylamine can be achieved quite readily through acquisition of the mau cluster by HGT.

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Mechanism of reaction of allylamine with the quinoprotein methylamine dehydrogenase.

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