Forms Of MAO Research Articles

Comparative Analysis of the Neurochemical Profile and MAO Inhibition Properties of N-(Furan-2-ylmethyl)-N-methylprop-2-yn-1-amine.

The regulation of brain monoamine levels is paramount for cognitive functions, and the monoamine oxidase (MAO A and B) enzymes play a central role in these processes. The aim of this study was to evaluate whether the procognitive properties exerted by propargylamine N-(furan-2-ylmethyl)-N-methylprop-2-yn-1-amine (F2MPA) are related to changes in monoamine content via MAO inhibition. In vivo microdialysis and ex vivo amine metabolite measurement demonstrated region-specific alterations in monoamine metabolism that differ from both of the classic MAO A and MAO B inhibitors, clorgyline and l-deprenyl, respectively. Although all the inhibitors (1 and 4 mg/kg) increased cortical serotonin tissue content, only F2MPA increased the levels of cortical noradrenaline. In the striatum, clorgyline (1 mg/kg), but not F2MPA (1 mg/kg), reduced extracellular levels of dopamine metabolites at rest or stimulated by the intrastriatal application of the MAO substrate 3-methoxytyramine. In vitro, F2MPA exhibited a low affinity toward MAO B and MAO A. Nonetheless, it modified the B form of MAO, forming a flavin adduct structurally similar to that with deprenyl. F2MPA was rapidly metabolized in the presence of rat but not human microsomes, producing a hydroxylated derivative. In conclusion, the effect of F2MPA on cognition may arise from monoaminergic changes in the cortex, but the role of MAO in this process is likely to be negligible, consistent with the poor affinity of F2MPA for MAO.

Kinetics and Growth of Polyethylene Nanofibrils over Metallocene Catalyst Supported on Flat Silica and Spherical Nano‐Silica Particles

AbstractThe kinetics of ethylene polymerization and the growth of polymer nanofibrils for the rac‐Et(indenyl)2 ZrCl2/MAO catalyst supported on flat‐surface silica and nonporous silica nanoparticles are presented. The polymerization rate per mol of Zr is highest for the flat‐silica supported catalyst due to maximum exposure of catalyst sites to cocatalyst and monomer. The SEM and AFM analysis show that large clusters of oxidized form of MAO are present at the surface, while nano‐silica supported catalyst show less of such effects. The polyethylene grows as nanofibrils of 30–50 nm in diameter from the silica surface. No particle fragmentation is observed with nano‐silica supported catalyst where polymer nanofibrils grow only from the external surface. Polymer properties are little affected by the support type.

The ‘gating’ residues Ile199 and Tyr326 in human monoamine oxidase B function in substrate and inhibitor recognition

The major structural difference between human monoamine oxidases A (MAO A) and B (MAO B) is that MAO A has a monopartite substrate cavity of ~550 Å(3) volume and MAO B contains a dipartite cavity structure with volumes of ~290 Å(3) (entrance cavity) and ~400 Å(3) (substrate cavity). Ile199 and Tyr326 side chains separate these two cavities in MAO B. To probe the function of these gating residues, Ile199Ala and Ile199Ala-Tyr326Ala mutant forms of MAO B were investigated. Structural data on the Ile199Ala MAO B mutant show no alterations in active site geometries compared with wild-type enzyme while the Ile199Ala-Tyr326Ala MAO B mutant exhibits alterations in residues 100-103 which are part of the loop gating the entrance to the active site. Both mutant enzymes exhibit catalytic properties with increased amine K(M) but unaltered k(cat) values. The altered K(M) values on mutation are attributed to the influence of the cavity structure in the binding and subsequent deprotonation of the amine substrate. Both mutant enzymes exhibit weaker binding affinities relative to wild-type enzyme for small reversible inhibitors. Ile199Ala MAO B exhibits an increase in binding affinity for reversible MAO B specific inhibitors which bridge both cavities. The Ile199Ala-Tyr326Ala double mutant exhibits inhibitor binding properties more similar to those of MAO A than to MAO B. These results demonstrate that the bipartite cavity structure in MAO B plays an important role in substrate and inhibitor recognition to distinguish its specificities from those of MAO A and provide insights into specific reversible inhibitor design for these membrane-bound enzymes.

Different stereoselective inhibition of monoamine oxidase-B by the R- and S-enantiomers of MD 780236.

MD 780236, a selective inhibitor of the B form of MAO behaves as an irreversible inhibitor in in-vitro conditions and mainly as a short-acting inhibitor in ex-vivo experiments. The enantiomer with the R absolute configuration (MD 240928) is fully reversible in ex-vivo conditions, whereas the S-enantiomer (MD 240931) has kept the irreversible component of the inhibition seen with MD 780236. The corresponding racemic alcohol derivative (MD 760548) is also a short-acting inhibitor of the B form of MAO; its S-enantiomer, which has an absolute configuration corresponding to that of MD 240928, has a selectivity towards the B form superior to that of the other enantiomer. The mechanism of the MAO inhibition by MD 780236 is discussed.

A monoamine oxidase-B inhibitor, MD 780236, metabolized essentially by the A form of the enzyme in the rat.

In-vivo studies on the metabolism of [14C]MD 780236 a short-acting selective type B MAO inhibitor in the rat showed the acid to be the major metabolite in plasma and urine, whereas it was minor in brain, where the alcohol was the major metabolite. Pretreatment with SKF 525-A did not modify the metabolite profile in brain, but benserazide decreased the alcohol. Pretreatment with (-)-selegiline had no effect, but clorgyline or clorgyline with (-)-selegiline significantly decreased the alcohol and increased the primary amine metabolite in brain. In-vivo results suggest that MAO-A is the enzyme responsible for the metabolism of MD 780236. This was confirmed by in-vitro studies. Rat brain homogenates extensively metabolized the drug, with the aldehyde being the major metabolite formed (28% of the total radioactivity in the incubation mixture after 60 min incubation). The acid (12%) was more important than the alcohol (4%) in-vitro. The addition of all metabolites originating from possible MAO activity gave 46% when the incubation was carried out at pH 7.4 and 82% at pH 8.8. The presence of NADPH or NAD+ did not alter the relative amounts of metabolites formed. Total metabolites originating from MAO activity in the presence of (-)-selegiline accounted for 40% of total radioactivity, whereas in the presence of clorgyline they accounted for 8% and in the presence of both clorgyline and (-)-selegiline they were reduced to 3%, compared with 45% in controls. As a further proof of the importance of MAO-A in the metabolism of MD 780236, rats were pretreated with clorgyline 1 h before the drug and MAO-B inhibition measured at different times ex-vivo in brain and liver. The short-lasting phase of inhibition of MAO-B disappeared after pretreatment with clorgyline, and inhibition at 24 h was as high as that at 1 h. These results demonstrate the importance of the A form of MAO for the metabolism of MD 780236.

CANDU reactor as minor actinide/thorium burner with uniform power density in the fuel bundle

A CANDU reactor fueled with a mixed fuel made of thoria (ThO 2) and nuclear waste actinides has been investigated. The mixed fuel composition has been varied in radial direction to achieve a uniform power distribution and fuel burn-up in the fuel bundle. The best fuel compositions with respect to power flattening as well as long term reactivity have been found by mixing thoria with 14% minor actinides in form of MAO 2 in the central fuel bundle and with a radially decreasing MAO 2 content at discrete levels down to 2% at the periphery. Furthermore, as an alternative fuel composition, 5% UO 2 has been added to the mixed fuel for the sake of a higher degree of nuclear safeguarding through denaturing the 233U component with 238U. The temporal variation of the criticality k ∞ and the burn-up values of the reactor have been calculated for a period of 10 years, operated at full power. The criticality starts at time zero near to k ∞ = ∼1.24 for both fuel compositions. A sharp decrease of the criticality has been observed during the first year as a consequence of rapid plutonium burnout in the actinide fuel. The criticality becomes quasi-constant after the 2nd year after sufficient 233U is accumulated and remains close to k ∞,end = ∼1.06 over ∼10 years. Quasi-uniform power generation density has been realized in the fuel bundle throughout the reactor operation. Very high burn-up could be achieved with the same fuel material (up to 200,000 MW D/MT), provided that the fuel rod claddings would be replaced periodically. This would reduce fuel fabrication costs and nuclear waste mass for final disposal per unit energy drastically.

Functional Role of the “Aromatic Cage” in Human Monoamine Oxidase B: Structures and Catalytic Properties of Tyr435 Mutant Proteins,

Current structural results of several flavin-dependent amine oxidizing enzymes including human monoamine oxidases A and B (MAO A and MAO B) show aromatic amino acid residues oriented approximately perpendicular to the flavin ring, suggesting a functional role in catalysis. In the case of human MAO B, two tyrosyl residues (Y398 and Y435) are found in the substrate binding site on the re face of the covalent flavin ring [Binda et al. (2002) J. Biol. Chem. 277, 23973-23976]. To probe the functional significance of this structure, Tyr435 in MAO B was mutated with the amino acids Phe, His, Leu, or Trp, the mutant proteins expressed in Pichia pastoris, and purified to homogeneity. Each mutant protein contains covalent FAD and exhibits a high level of catalytic functionality. No major alterations in active site structures are detected on comparison of their respective crystal structures with that of WT enzyme. The relative k(cat)/K(m) values for each mutant enzyme show Y435 > Y435F = Y435L = Y435H > Y435W. A similar behavior is also observed with the membrane-bound forms of MAO A and MAO B (MAO A Y444 mutant enzymes are found to be unstable on membrane extraction). p-Nitrobenzylamine is found to be a poor substrate while p-nitrophenethylamine is found to be a good substrate for all WT and mutant forms of MAO B. Analysis of these kinetic and structural data suggests the function of the "aromatic cage" in MAO to include a steric role in substrate binding and access to the flavin coenzyme and to increase the nucleophilicity of the substrate amine moiety. These results are consistent with a proposed polar nucleophilic mechanism for catalytic amine oxidation.

Synthesis and biological evaluation of 3-alkyloxazolidin-2-ones as reversible MAO inhibitors

The discovery of the two forms of MAO had led to significant advances in the understanding of the physiological and biochemical roles that these enzymes play in normal processes and in disease states. The recent development of a new generation of highly selective reversible MAO inhibitors (MAOIs) have led to a renewed interest in the therapeutic potential of these new compounds with respect to early irreversible MAOIs. In fact, reversible MAOIs offer new hopes for generating superior anti-depressant and anti-parkinsonian agents by virtue of the selective inhibition of MAO-A and MAO-B, respectively. Aryloxazolidinones are one of the relatively new classes of MAOIs. Their lead compound is Toloxatone (Humoryl®), the first reversible and selective MAO-A inhibitor introduced in clinical practice as an anti-depressant. In order to investigate the importance and hence the biological role played by the anisyl (p-methoxyphenyl) group linked to N3 atom of Toloxatone oxazolidinone ring or more in general of an aromatic group, some new N3-alkyloxazolidinones were synthesized and their ability to inhibit MAO-A and MAO-B enzymes was evaluated by a fluorimetric method that uses the kynuramine as substrate. Also modifications at C5 of the 2-oxazolidinone ring were considered. The set of N3- alkyl substituted and at C5 modified compounds showed ability to inhibit MAO-A and MAO-B but with lower extent than Toloxatone used as reference drug. Such biological results provide insights into structure-activity relationships, confirming that is necessary the presence of N3-aryl moiety to act as a potent reversible MAO inhibitor, not possible in the same extent when the aryl is replaced by an alkyl group (Ki≈ 10 -7 M versus 10 -3 -10 -4 M).

Monoamine oxidase B inhibition and neuroprotection

The principal therapeutic agents used in the management of Parkinson's disease (PD) enhance nigrostriatal dopaminergic flux through either replenishment of depleted dopamine stores or the action of dopaminergic agonists. Adenosine A2A receptor antagonists (e.g., KW-6002) may provide symptomatic relief in PD and perhaps also may display neuroprotective properties based on studies in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of nigrostriatal neurodegeneration. A second class of compounds that is neuroprotective in the MPTP model comprises inhibitors of the outer mitochondrial flavoenzyme monoamine oxidase B (MAO B), one of the two forms of MAO that regulate levels of brain neurotransmitter substances, including dopamine. In this article, data are presented that document the overlapping A2A antagonist and MAO B inhibitory properties of several 2-styrylxanthinyl derivatives. A limited structure-activity analysis of these compounds and structurally related analogs is provided. The results raise the possibility that a single structure may offer the combined benefits of two pharmacologic strategies, each with symptomatic and potential neuroprotective benefits, for the management of PD.

A theoretical study of the insertion barrier of MAO methylaluminoxane)-activated, Cp2ZrMe2-catalyzed ethylene polymerization: further evidence for the structural assignment of active and dormant species.

Density functional theory has been used to calculate the ethylene insertion barrier into the Zr-C bonds of the [Cp2ZrMe](+)[AlMe3Me(A-MAO)]- and [Cp2ZrMe](+)[Me(A-MAO)]- ion pairs where (AlOMe)6 was used to model the active forms of MAO (A-MAO). The results support the proposal that the former is the active and the latter the dormant species in MAO-activated olefin polymerization. For the first insertion, with the active species the trans approach has a lower barrier to insertion than the cis approach in solution, due to the larger ion pair separation. It is likely that the separated ion pairs recombine between subsequent insertions. For the second insertion, we have considered frontside, backside and combined insertion mechanisms showing that the total barrier to insertion is approximately the same in all cases ranging from 13.8 kcal mol(-1)-14.8 kcal mol(-1). For the frontside and combined insertion this barrier is a result of the rotation of the propyl chain: for the backside mechanism it is stems from the ethylene insertion barrier. Comparison of the results for the ion pair and for the naked cation show that in the former case olefin complexation is an endothermic process whereas for the latter it is exothermic. In general, the large ion pair separation prevents the orientation of the anion from exerting much influence on the geometry or energy of the cation. However, when structures with alpha-agostic interactions are considered the ion pair separation is small enough so that the orientation has some influence on the reaction mechanism. For the second insertion, dissociated transition states were found to have lower barriers than associated ones.

Monoamine oxidase in Teleosts

The main aim of this paper is to provide an overview of the characteristics, function and distribution of monoamine oxidase activity in fish. Studies on MAO performed in different classes of terrestrial vertebrates have demonstrated that MAO is represented by two isoenzymes called MAO A and MAO B. By contrast, in fish, monoamine oxidase does not fit into the classical MAO A/MAO B binary classification. Most of the research carried out so far on fish has concerned Teleosts. In all the species examined it has been found that MAO activity is due to a single form of MAO. In several species, this form has been classified as MAO A. In other species it has been considered as a novel form, distinct from both MAO A and MAO B. This latter view has been confirmed in trout by cloning MAO cDNA from liver. The second part of the present review deals with the literature data on the hormonal effects on brain MAO activity in fish. In particular, significant effects on hypothalamic MAO activity were caused by estradiol. Lastly, a summary is provided of studies on the effects induced by heavy metals and organic compounds on fish brain MAO activity. These pollutants can alter brain MAO activity to different degrees and such effects could interfere indirectly with gonad maturation and thus with reproductive capacity.

In vitro biotransformation of the selective serotonin reuptake inhibitor citalopram, its enantiomers and demethylated metabolites by monoamine oxidase in rat and human brain preparations.

This study was conducted to identify enzyme systems eventually catalysing a local cerebral metabolism of citalopram, a widely used antidepressant of the selective serotonin reuptake inhibitor type. The metabolism of citalopram, of its enantiomers and demethylated metabolites was investigated in rat brain microsomes and in rat and human brain mitochondria. No cytochrome P-450 mediated transformation was observed in rat brain. By analysing H2O2 formation, monoamine oxidase A activity in rat brain mitochondria could be measured. In rat whole brain and in human frontal cortex, putamen, cerebellum and white matter of five brains monoamine oxidase activity was determined by the stereoselective measurement of the production of citalopram propionate. All substrates were metabolised by both forms of MAO, except in rat brain, where monoamine oxidase B activity could not be detected. Apparent Km and Vmax of S-citalopram biotransformation in human frontal cortex by monoamine oxidase B were found to be 266 microM and 6.0 pmol min(-1) mg(-1) protein and by monoamine oxidase A 856 microM and 6.4 pmol min(-1) mg(-1) protein, respectively. These Km values are in the same range as those for serotonin and dopamine metabolism by monoamine oxidases. Thus, the biotransformation of citalopram in the rat and human brain occurs mainly through monoamine oxidases and not, as in the liver, through cytochrome P-450.

Selective Inhibition of Monoamine Oxidase B by Aminoethyl Substituted Benzyl Ethers

Aminoethyl 3-chlorobenzyl ether was shown previously (Ding, C.Z. and Silverman, R.B. (1993). Bioorg. Med. Chem. Lett., 3, 2077-2078) to be a potent and selective time-dependent, but reversible inhibitor of monoamine oxidase B (MAO B). Based on this result, a series of novel aminoethyl substituted benzyl ethers was synthesized and the compounds were examined as potential inhibitors of both isozymic forms of MAO. Each compound in the series inhibits both MAO A and MAO B competitively, and IC50 values for each compound were determined. In general, the B isozyme is much more sensitive to these inhibitors than the A isozyme (except for the o- and p-substituted nitro analogues), in some cases by more than two orders of magnitude. The selectivity in favor of MAO B inhibition is relatively high for all of the meta-substituted analogues and quite low for all of the ortho-substituted analogues. Having the substituent at the ortho-position is most favorable for MAO A inhibition. With MAO B the meta-analogues were, in general, more potent than the corresponding ortho- and para-analogues with respect to their reversible binding constants. The meta-iodo analogue is the most potent analogue.

Monoamine oxidase catalysis on electrodes modified with artificial acceptors of electrons

Catalytic properties of monoamine oxidase B-type (MAO-B) were studied on electrodes modified with artificial acceptors of electrons (AAE). It has been shown that AAE can substitute of oxygen in enzymatic reaction of amines oxidation. Some organic compounds were examined, namely 7,7′,8,8′-tetracyanoquinodimethane (TCNQ), methyl-1,4-benzoquinone (MBQ), 1,4-naphthoquinone (NQ) and phenazine methosulfate (PMS). At anaerobic conditions in the system containing MAO-B and its specific substrate benzylamine (BA) an abrupt increase of the anodic current was observed for TCNQ, MBQ and NQ adsorbed on the electrode. The current did not increase when MAO was replaced with bovine serum albumine or enzyme was inactivated by MAO-B specific inhibitor deprenyl. The dependence of the anodic current on concentrations of AAE (TCNQ, MBQ and NQ) and benzylamine was detected. It was demonstrated that TCNQ as well as MBQ and NQ act as MAO substrates which are capable to substitute an oxygen in the catalytic reaction at anaerobic conditions. It was found that PMS hardly interacts with reduced form of MAO though this compound posses good electromediator properties.

Role of selegiline in combination therapy of Parkinson's disease.

Selegiline (earlier called deprenyl) is an irreversible inhibitor of monoamine oxidase type B (MAO-B). The inhibition is based on a covalent, irreversible bond formed between the propargyl group of selegiline and the flavin part of MAO. [1] In low doses (0.25 mg/kg subcutaneously in rats and 10 mg daily in humans) selegiline is a potent and selective inhibitor of MAO-B. [2,3] MAO-B inhibition can be easily tested in humans by measuring the MAO activity of platelets, as about 95% of MAO activity in platelets is of type B. [4] Because of its selectivity it is free of the cheese effect, i.e., increase of blood pressure after food rich in tyramine, which is a substrate for MAO-A. [5,6] In rodents selegiline does not have marked effects on the concentrations of the main catecholamines, dopamine or noradrenaline, because MAO-A is the predominant form of MAO in rodent brain. [7] In primate brain MAO-B is the predominant form with regard to degradation of dopamine, and therefore selegiline causes an increase of dopamine and decrease of 3,4-dihydroxyphenylacetic acid (DOPAC) in caudate in monkey brain. [8] In parkinsonian rat models, such as the 6-hydroxy dopamine (6-OHDA) model in which substantia nigra has been unilaterally destroyed with the toxin, selegiline enhances the effect of levodopa. [9-11] Nonselective MAO inhibitors had earlier been reported to cause some benefit but unacceptable adverse events in the treatment of Parkinson's disease (PD), [12,13] and therefore it was logical to test selegiline in this disease. The early findings by Birkmayer et al. [14] showed that selegiline potentiated the efficacy of levodopa in the treatment of PD patients and was well tolerated. This preliminary finding was followed by a number of trials assessing selegiline therapy in PD. The studies first concentrated on the use of selegiline in advanced PD, i.e., patients with …

Monoamine oxidase B isolated from bovine liver exists as large oligomeric complexes in vitro.

The quaternary structure and subunit composition of bovine liver monoamine oxidase B (MAO B) was investigated using size-exclusion chromatography, sucrose gradient centrifugation and electron microscopy. Purified enzyme was subjected to Superdex gel filtration column chromatography in the presence of the non-ionic detergents, n-octyl beta-D-glucopyranoside (octyl glucoside) and Triton X-100R-PC (Triton). The specific activity and elution profiles indicate that the enzyme exists as a dimer and preferentially functions as larger oligomeric complexes. Distribution of the oligomeric forms of MAO B was found to be dependent upon protein concentration. Dilution of the enzyme, however, had little or no effect upon the specific activity profiles. In Triton and octyl glucoside, plots of specific activity versus molecular mass displayed a sigmoidal shape. The chromatographic data suggest that detergent-solubilized bovine liver MAO B exists as cooperative oligomeric enzyme complexes. Similarly, sucrose density gradient centrifugation of purified MAO B exhibited a direct correlation between enzyme activity and molecular mass of the MAO complexes. MAO B activity was found to be widely distributed throughout the sucrose gradient and the highest enzyme activity was contained in the high-density sucrose layers. MAO B specific activity is dependent upon the size of the protein complexes and, therefore, oligomerization of the enzyme may play a role in the regulation of MAO B. Transmission electron microscopy of purified MAO B was performed using protein prepared by octyl glucoside extraction. Purified enzyme was applied to Formvar-coated copper grids and negatively stained with methylamine tungstate. MAO-B-specific monoclonal antibody (MAO B-1C2) conjugated to colloidal gold was used as a probe. Contrast enhancement of the electron microscopy data showed that detergent-depleted enzyme tends to aggregate in a linear arrangement of oligomeric complexes. Our data suggest that the MAO B oligomeric complexes are hexamers which contain threefold rotational symmetry. The individual complexes have globular morphology and the hexamers appear to be composed of a trimer of MAO B homodimers.

Studies on the nature of the antagonistic actions of dopamine and 5-hydroxytryptamine in renal tissues.

The present work examines the possibility of whether the reciprocal effects of dopamine (DA) and 5-hydroxytryptamine (5-HT) are only dependent on the antagonistic nature of the signal resulting from the activation of their specific receptors or may also result from a competitive type of inhibition at different levels of the synthetic and metabolic pathways shared by DA and 5-HT. Studies performed in isolated proximal convoluted tubules (PCT) have shown that L-5-HTP and L-DOPA use the same transporter in order to be taken up into the cell and both L-DOPA and L-5-HTP exert a competitive type of inhibition upon their cellular uptake. The decrease in the formation of 5-HT in isolated PCT induced by L-DOPA reflects most probably a reduction in the intracellular availability of L-5-HTP. However, in experiments conducted in homogenates of PCT L-DOPA was found to be a better substrate for AAAD than L-5-HTP. Apart from sharing a common synthetic pathway, DA and 5-HT also share a common metabolic pathway; type A monoamine oxidase (MAO-A), the predominant form of MAO in rat renal tissues, converts DA into 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-HT into 5-hydroxyindolacetic acid (5-HIAA). However, in contrast to 5-HT, DA can be metabolized by MAO-B and catechol-O-methyltransferase. Inhibition of MAO-A was found to produce a 2-fold increase in the urinary excretion of 5-HT; this increase in the urinary excretion of 5-HT was accompanied by an unexpected reduction in the urinary excretion of DA.(ABSTRACT TRUNCATED AT 250 WORDS)

Monoamine oxidase inhibitors increase preferentially extracellular 5-hydroxytryptamine in the midbrain raphe nuclei. A brain microdialysis study in the awake rat.

We have examined the local and systemic effects of clorgyline, tranylcypromine and deprenyl on extracellular serotonin (5-HT) and 5-hydroxyindoleacetic acid in the raphe nuclei and in frontal cortex of awake, freely-moving rats using microdialysis. When administered through the dialysis probe, monoamine oxidase (monoamine: oxygen oxidoreductase (deaminating), E.C. 1.4.3.4., MAO) inhibitors increased 5-HT output in a dose-dependent manner in both brain areas. The effects were more pronounced in the raphe nuclei for the three MAO inhibitors at all doses assayed. When the monoamine oxidase inhibitors were given i.p., dialysate 5-HT increased dramatically, after tranylcypromine (15 mg/kg), in raphe nuclei and frontal cortex (area under the curve (AUC) to 4 h post-treatment: 63-fold and 11-fold, respectively) whereas the effects of clorgyline (10 mg/kg) were much less pronounced (+47% increase in the AUC for raphe nuclei, P < 0.09; +18% increase in the AUC for frontal cortex, n.s.). Deprenyl (2.5 mg/kg, i.p.) induced a moderate (+22%) increase of dialysate 5-HT from the raphe nuclei but did not cause a change in dialysate 5-HT from the frontal cortex (+4%). However, clorgyline, or deprenyl, dramatically increased dialysate 5-HT in animals which had been pre-treated with the above dose of deprenyl, or clorgyline, respectively, showing that the blockade of both forms of MAO results in much larger increases of extracellular 5-HT than does the blockade of either form alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Resonance Raman Spectroscopic Evidence for an Anionic Flavin Semiquinone in Bovine Liver Monoamine Oxidase

The flavoprotein monoamine oxidase B (MAO B) from bovine liver, as isolated, has an unusual additional absorption band at 412 nm, which is similar to the absorption of its anionic flavin semiquinone form, (Fl∸), and other typical (Fl∸) flavoproteins. Denatu ration of the enzyme results in the elimination of this anomalous absorption. The resonance Raman (RR) spectrum of MAO B as isolated is virtually identical to that of its dithionitereduced (Fl∸) form. Both spectra show features similar to those of the RR spectrum of the (Fl∸) form of Aspergillus niger glucose oxidase (GO) in the region between 300 and 1700 cm−1 with 406.7 nm excitation. These features are readily distinguishable from those of oxidized flavin, neutral fiavin semiquinone, and hemoprotein, strongly suggesting the presence of an (Fl∸) form in MAO B as isolated, even with preparations isolated in the absence of light. There are significant differences between the RR spectra of the (Fl∸) form of MAO B and those of GO or the published RR spectra of the (Fl∸) form of Damino acid oxidase with excess substrate analog. At least some of these differences can be attributed to the different binding of flavin in the three enzymes. No EPR signals due to (Fl∸) are observed in MAO B as isolated. The dithionite-reduced (Fl∸) form exhibits 50% less EPR signal than that expected from the absorption spectrum, which suggests a possible coupling of the (Fl∸) fiavin with a paramagnetic center of unknown identity in the protein. The implications of these observations on MAO B with the current view of its catalytic mechanism are discussed.

Monoamine oxidase, dopamine and Parkinson's disease

Four aspects about monoamine oxidase (MAO; E.C. 1.4.3.4) are of obvious interest in relation to Parkinson's disease and its treatment with the irreversible and selective MAO-B inhibitor L-deprenyl and are discussed in this review: 1) To what extent the two forms of MAO are of importance for the deamination of dopamine and to what degree MAO localised inside and outside of dopaminergic nerve terminals contributes 2) The kinetics of the MAO-protein, i.e. the rate of recovery of MAO after irreversible inhibition. 3) To what extent MAO may be changed as a consequence of the pathophysiological processes. 4) To what extent MAO may be involved as a force in the pathophysiological processes.