title: Reactions of benzylamines with methylamine dehydrogenase. Evidence for a carbanionic reaction intermediate and reaction mechanism similar to eukaryotic quinoproteins.
abstract: It had been previously reported that aromatic amines were not substrates for the bacterial quinoprotein methylamine dehydrogenase. In this study, benzylamine-dependent activity was also not observed in the steady-state assay of this enzyme with the artificial electron acceptor phenazine ethosulfate (PES). Benzylamines did, however, stoichiometrically reduce the protein-bound tryptophan tryptophylquinone (TTQ) prosthetic group and acted as reversible competitive inhibitors of methylamine oxidation when the enzyme was assayed with PES. When methylamine dehydrogenase activity was monitored using a steady-state assay which employed its physiological electron acceptor amicyanin instead of PES, very low but detectable benzylamine-dependent activity was observed. The reactions of a series of para-substituted benzylamines with methylamine dehydrogenase were examined. A Hammett plot of the log of Ki values for the competitive inhibition by these amines against sigma p exhibited a negative slope. Rapid kinetic measurements allowed the determination of values of k3 and Ks for the reduction of TTQ by each of these amines. A Hammett plot of log k3 versus sigma p exhibited a positive slope, which suggests that the oxidation of these amines by methylamine dehydrogenase proceeds through a carbanionic reaction intermediate. A negative slope was observed for the correlation between log Ks and sigma p. Plots of log k3 and log Ks against substituent constants which reflected either resonance or field/inductive parameters for each para substituent indicated that the magnitude of k3 was primarily influenced by field/inductive effects while Ks was primarily influenced by resonance effects. No correlation was observed between either k3 or Ks and the relative hydrophobicity of the para-substituted benzylamines or steric parameters.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Biochemistry, University of Mississippi Medical Center, Jackson 39216-4505.
authors.forename: V L
authors.initials: VL
authors.lastname: Davidson
authors.forename: L H
authors.initials: LH
authors.lastname: Jones
authors.forename: M E
authors.initials: ME
authors.lastname: Graichen
mesh_terms: D000838:Anions; D001426:Bacterial Proteins / Q000378:metabolism; D001596:Benzylamines / Q000494:pharmacology*; D001667:Binding, Competitive; D004579:Electron Transport; D045563:Indolequinones; D007700:Kinetics; D010084:Oxidation-Reduction; D000587:Oxidoreductases Acting on CH-NH Group Donors / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010231:Paracoccus denitrificans / Q000201:enzymology; D010619:Phenazines / Q000378:metabolism; D011809:Quinones / Q000378:metabolism*; D013053:Spectrophotometry; D014364:Tryptophan / Q000031:analogs & derivatives / Q000378:metabolism
chemical_list: D000838:Anions; D001426:Bacterial Proteins; D001596:Benzylamines; D045563:Indolequinones; D010619:Phenazines; D011809:Quinones; C017079:mauC protein, Methylobacterium extorquens; C028122:5-ethylphenazine; C070569:tryptophan tryptophylquinone; D014364:Tryptophan; C021567:methylamine dehydrogenase; D000587:Oxidoreductases Acting on CH-NH Group Donors