Publications

• Mechanistic studies of aromatic amine dehydrogenase, a tryptophan tryptophylquinone enzyme.

  Hyun Y.L., Davidson V.L.

  Aromatic amine dehydrogenase (AADH) is the second enzyme known to possess the tryptophan tryptophylquinone (TTQ) prosthetic group. Its ability to catalyze the oxidative deamination of a wide range of aromatic and aliphatic amines has been investigated. Steady-state and transient kinetic studies of ... >> More

  Aromatic amine dehydrogenase (AADH) is the second enzyme known to possess the tryptophan tryptophylquinone (TTQ) prosthetic group. Its ability to catalyze the oxidative deamination of a wide range of aromatic and aliphatic amines has been investigated. Steady-state and transient kinetic studies of the reaction of AADH with a series of p-substituted phenylethylamines were performed to determine structure-reactivity correlations. The Km values correlated strongly with hydrophobic effects. The microscopic rate constant associated with TTQ reduction, k3, correlated with electronic substituent effects, particularly field/inductive effects, in a manner consistent with the formation of a carbanionic reaction intermediate in the reductive half-reaction. Transient kinetic studies were also performed with a series of p-substituted benzylamines, which were not substrates in the steady-state assay, but which did stoichiometrically reduce TTQ. The k3 for the reaction with benzylamines also correlated well with electronic effects. The rate constant associated with the release of the aldehyde product was also determined for the phenylethylamines and appears to be the most rate-limiting step in the overall oxidation-reduction reaction. This rate constant correlated with hydrophobic amines. This substrate specificity for aliphatic amines is opposite of that of methylamine dehydrogenase (MADH), the other known TTQ enzyme. On the basis of these studies, a reaction mechanism is proposed for AADH. These data are discussed in relation to the results of structure-reactivity correlation studies of the reactions catalyzed by MADH and two eukaryotic quinoproteins with different quinone prosthetic groups, plasma amine oxidase and lysyl oxidase. << Less

  Biochemistry 34:816-823(1995) [PubMed] [EuropePMC]

• Aromatic amine dehydrogenase, a second tryptophan tryptophylquinone enzyme.

  Govindaraj S., Eisenstein E., Jones L.H., Sanders-Loehr J., Chistoserdov A.Y., Davidson V.L., Edwards S.L.

  Aromatic amine dehydrogenase (AADH) catalyzes the oxidative deamination of aromatic amines including tyramine and dopamine. AADH is structurally similar to methylamine dehydrogenase (MADH) and possesses the same tryptophan tryptophylquinone (TTQ) prosthetic group. AADH exhibits an alpha 2 beta 2 s ... >> More

  Aromatic amine dehydrogenase (AADH) catalyzes the oxidative deamination of aromatic amines including tyramine and dopamine. AADH is structurally similar to methylamine dehydrogenase (MADH) and possesses the same tryptophan tryptophylquinone (TTQ) prosthetic group. AADH exhibits an alpha 2 beta 2 structure with subunit molecular weights of 39,000 and 18,000 and with a quinone covalently attached to each beta subunit. Neither subunit cross-reacted immunologically with antibodies to the corresponding subunits of MADH, and the N-terminal amino acid sequence of the beta subunit of AADH exhibited no homology with the highly conserved beta subunits of MADH. The absorption spectra for the oxidized, semiquinone, and reduced forms of AADH have been characterized, and extinction coefficients for the absorption maxima of each redox form have been determined. These spectra are very similar to those for MADH, indicating the likelihood of a TTQ cofactor. This was verified by the near identity of the vibrational frequencies and intensities in the resonance Raman spectra for the oxidized forms of AADH and MADH. A stable semiquinone of AADH could be observed during a reductive titration with dithionite, whereas titration with tyramine proceeded directly from the oxidized to the reduced form. AADH was very stable against denaturation by heat and exposure to guanidine. The individual subunits could be separated by gel filtration after incubation in guanidine hydrochloride, and partial reconstitution of activity was observed on recombination of the subunits. Steady-state kinetic analysis of AADH yielded a Vmax of 17 mumol/min/mg and a Km for tyramine of 5.4 microM. Substrate inhibition by tyramine was observed. AADH was irreversibly inhibited by hydrazine, phenylhydrazine, hydroxylamine, semicarbazide, and aminoguanidine. Isonicotinic acid hydrazide (isoniazid) and isonicotinic acid 2-isopropyl hydrazide (iproniazid) were reversible noncompetitive inhibitors of AADH and exhibited K(i) values of 8 and 186 microM, respectively. The similarities and differences between AADH and other amine oxidizing enzymes are also discussed. << Less

  J. Bacteriol. 176:2922-2929(1994) [PubMed] [EuropePMC]