Publications

• How Monoamine Oxidase A Decomposes Serotonin: An Empirical Valence Bond Simulation of the Reactive Step.

  Prah A., Purg M., Stare J., Vianello R., Mavri J.

  The enzyme-catalyzed degradation of the biogenic amine serotonin is an essential regulatory mechanism of its level in the human organism. In particular, monoamine oxidase A (MAO A) is an important flavoenzyme involved in the metabolism of monoamine neurotransmitters. Despite extensive research eff ... >> More

  The enzyme-catalyzed degradation of the biogenic amine serotonin is an essential regulatory mechanism of its level in the human organism. In particular, monoamine oxidase A (MAO A) is an important flavoenzyme involved in the metabolism of monoamine neurotransmitters. Despite extensive research efforts, neither the catalytic nor the inhibition mechanisms of MAO enzymes are currently fully understood. In this article, we present the quantum mechanics/molecular mechanics simulation of the rate-limiting step for the serotonin decomposition, which consists of hydride transfer from the serotonin methylene group to the N5 atom of the flavin moiety. Free-energy profiles of the reaction were computed by the empirical valence bond method. Apart from the enzymatic environment, the reference reaction in the gas phase was also simulated, facilitating the estimation of the catalytic effect of the enzyme. The calculated barrier for the enzyme-catalyzed reaction of 14.82 ± 0.81 kcal mol^-1 is in good agreement with the experimental value of 16.0 kcal mol^-1, which provides strong evidence for the validity of the proposed hydride-transfer mechanism. Together with additional experimental and computational work, the results presented herein contribute to a deeper understanding of the catalytic mechanism of MAO A and flavoenzymes in general, and in the long run, they should pave the way toward applications in neuropsychiatry. << Less

  J Phys Chem B 124:8259-8265(2020) [PubMed] [EuropePMC]

• 90 years of monoamine oxidase: some progress and some confusion.

  Tipton K.F.

  It would not be practical to attempt to deal with all the advances that have informed our understanding of the behavior and functions of this enzyme over the past 90 years. This account concentrates key advances that explain why the monoamine oxidases remain of pharmacological and biochemical inte ... >> More

  It would not be practical to attempt to deal with all the advances that have informed our understanding of the behavior and functions of this enzyme over the past 90 years. This account concentrates key advances that explain why the monoamine oxidases remain of pharmacological and biochemical interest and on some areas of continuing uncertainty. Some issues that remain to be understood or are in need of further clarification are highlighted. << Less

  J Neural Transm (Vienna) 125:1519-1551(2018) [PubMed] [EuropePMC]

  This publication is cited by 6 other entries.

• Substrate-specific enhancement of the oxidative half-reaction of monoamine oxidase.

  Tan A.K., Ramsay R.R.

  Monoamine oxidases A and B have identical flavin sites but different, although overlapping, amine substrate specificity. Reoxidation of ternary complexes containing substrate is much faster than of free enzyme, and the enhancement is greater in the A form than the B form. The oxidative half-reacti ... >> More

  Monoamine oxidases A and B have identical flavin sites but different, although overlapping, amine substrate specificity. Reoxidation of ternary complexes containing substrate is much faster than of free enzyme, and the enhancement is greater in the A form than the B form. The oxidative half-reaction was studied with a variety of substrates to elucidate the specificity of the effect and to probe the different influences of substrate on the flavin reoxidation in the two forms of the enzyme. The second-order rate constant for the reoxidation was highest with monoamine oxidase A when kynuramine was the ligand (508 x 10(3) M-1 s-1) compared to 4 x 10(3) M-1 s-1 in its absence. MPTP (166 x 10(3) M-1 s-1) also enhanced reoxidation well, but indole substrates stimulated only poorly (e.g., tryptamine, 29 x 10(3) M-1 s-1; serotonin, 50 x 10(3) M-1 s-1). For the A form, the reduction of the flavin was rate-limiting in all cases. For the B form, reoxidation was rate-limiting for beta-phenylethylamine and contributed to the determination of the overall rate with several substrates. The ratio of the enhanced rate of oxidation to the rate of reduction correlated with the redox state of the enzyme in turnover experiments. All the observations are consistent with alternate paths of reoxidation, via either free enzyme or a reduced enzyme-substrate complex. The flux through each path is determined by the relative dissociation constants and rate constants. << Less

  Biochemistry 32:2137-2143(1993) [PubMed] [EuropePMC]

  This publication is cited by 5 other entries.

• A key amino acid responsible for substrate selectivity of monoamine oxidase A and B.

  Tsugeno Y., Ito A.

  Monoamine oxidase (MAO) oxidizes biologically important amines including neurotransmitters and plays a central role in the regulation of intracellular level of these amines. Two distinct forms of MAO (MAO A and MAO B) were defined based on differences in substrate and inhibitor specificities. We e ... >> More

  Monoamine oxidase (MAO) oxidizes biologically important amines including neurotransmitters and plays a central role in the regulation of intracellular level of these amines. Two distinct forms of MAO (MAO A and MAO B) were defined based on differences in substrate and inhibitor specificities. We earlier reported that the region between about residues 120 and 220 of rat MAO is responsible for determination of the substrate selectivity of MAO A and B (Tsugeno, Y. Hirashiki, I., Ogata, F., and Ito, A. (1995) J. Biochem. (Tokyo) 118, 974-980). To determine the essential amino acids in this region that participate in substrate recognition, a series of mutant enzymes in which amino acid residues that are conserved among various species but are different between the two forms of the enzyme were replaced with the corresponding amino acids of the counterpart and were engineered from the cDNAs of rat liver MAO A and B, and affinities for several substrates were examined. A single mutation in which Phe-208 in MAO A was substituted by the corresponding residue of Ile in MAO B was sufficient to convert the A-type substrate selectivity, and the reverse was exactly the case. Phe at this position was replaceable with Tyr for the A-type specificity and Ile was replaceable with Val and Ala for the B-type. Thus, aromatic and aliphatic residues seem to contribute to render substrate selectivity of MAO A and MAO B, respectively. << Less

  J. Biol. Chem. 272:14033-14036(1997) [PubMed] [EuropePMC]

  This publication is cited by 3 other entries.

• The oxidation of adrenaline and noradrenaline by the two forms of monoamine oxidase from human and rat brain.

  O'Carroll A.M., Bardsley M.E., Tipton K.F.

  The selective monoamine oxidase inhibitors clorgyline and (?)-deprenyl were used to study the distribution of monoamine oxidase-A and -B (MAO-A, MAO-B) activities towards (?)-noradrenaline and (+),(?)-adrenaline in homogenates from seven different regions of human brain. The activities towards 5-h ... >> More

  The selective monoamine oxidase inhibitors clorgyline and (?)-deprenyl were used to study the distribution of monoamine oxidase-A and -B (MAO-A, MAO-B) activities towards (?)-noradrenaline and (+),(?)-adrenaline in homogenates from seven different regions of human brain. The activities towards 5-hydroxytryptamine and 2-phenethylamine, which are essentially specific substrates for the A- and B-forms, respectively, under the conditions used in this work, were also determined. Noradreanline and adrenaline were substrates for both forms of the enzyme in all regions studied. The total MAO activity was found to be highest in the hypothalamus and lowest in the cerebellar cortex. Use of the selective MAO inhibitors clorgyline and (?)-deprenyl also showed adrenaline and noradrenaline to be substrates for both forms of the enzyme in rat brain. In human cerebral cortex and rat brain the two forms were found to have similar K(m)-values and maximum velocities towards adrenaline. These values for the two forms were also found to be similar in human cerebral cortex when noradrenaline was used as the substrate. In contrast MAO-A showed a significantly lower K(m) and a higher maximum velocity towards noradrenaline in rat brain. These results suggest that the rat may not provide a close model of the human for studies on the effects of MAO inhibitors on brain noradrenaline metabolism. << Less

  Neurochem. Int. 8:493-500(1986) [PubMed] [EuropePMC]

  This publication is cited by 5 other entries.