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PubMed1980

Partial characterization of monoamine oxidase in the salivary gland of rats.

Changes in the substrate specificity of monoamine oxidase in the rat submaxillary gland were examined after ligation of the excretory duct and after denervation by postganglionic sympathectomy. Atrophy of the parenchymal cells after ligation of the excretory duct was observed, but such was not so clear after the denervation. The rate of decreases in the enzyme activity after the duct ligation was highest with serotonin, intermediate with dopamine and tyramine and lowest with beta-phenylethylamine, used as substrates. The proportion of form A monoamine oxidase was examined using clorgyline as an inhibitor specific for form A enzyme; approximately 95%, 90% and 85% of the total enzyme activities were attributed to form A enzyme in the intact glands, in the denervated glands and in the duct ligated glands, respectively. These results indicate that 90% of the enzyme activity in the parenchymal cells and almost of all the enzyme activity in the sympathetic nerves of the gland may be attributed to form A enzyme and the atrophy of parenchymal cells after the duct ligation results in a decrease in form A enzyme more markedly than form B.

Animals↗

PubMed1983

[Kinetics of the inhibition of mitochondrial monoamine oxidases A and B from rat liver by 1-(indolyl-3)isopropylmethylpropargylamine].

The kinetics of inhibition of the activity of monoamine oxidases A (with 5-oxytryptamine as substrate) and B (with 2-phenylethylamine as substrate) from rat liver mitochondria by a new acetyleneamine, 1-(indolyl-3)isopropylmethylpropargylamine, was studied. It was shown that the inhibition of the both forms of monoamine oxidase results in formation of an intermediate dissociating enzyme--inhibitor complex which is further converted into an irreversibly blocked enzyme. The value of the dissociation constant, Ki, of the intermediate enzyme--inhibitor complex with 2-phenylethylamine as substrate is equal to 24 . 10(6) M, that with 5-oxytryptamine--to 0.09 . 10(-6) M. The values of the rate constants, K3, for the conversion of the enzyme--inhibitor complex into an irreversibly blocked enzyme in experiments with 2-phenylethylamine and 5-oxytryptamine were rather close, i. e. 0.06 and 0.05 min-1, respectively. The results obtained indicate that the selectivity and inhibition of the activity of monoamine oxidases A and B by propargylamine derivatives is manifested at the primary step of formation of dissociating intermediate enzyme--inhibitor complexes.

Animals↗

PubMed1995

Cloning, sequencing and heterologous expression of the monoamine oxidase gene from Aspergillus niger.

The gene encoding the flavin-containing monoamine oxidase (MAO-N) of the filamentous fungus Aspergillus niger was cloned. MAO-N is the first nonvertebrate monoamine oxidase described to date. Three partial cDNA clones, isolated from an expression library, were used to identify and clone the structural gene (maoN) from an A. niger genomic DNA library. The maoN gene was sequenced, and analysis revealed an open reading frame that codes for a protein of 495 amino acids with a calculated molecular mass of 55.6 kDa. Sequencing of an internal proteolytic fragment of the purified enzyme confirmed the derived amino acid sequence. Analysis of the deduced amino acid sequence indicates that MAO-N is structurally related to the human monoamine oxidases MAO-A and MAO-B. In particular, the regions known to be involved in the binding of the FAD cofactor show a high degree of homology; however, the conserved cysteine residue to which the flavin cofactor is covalently bound in the mammalian forms is absent in the fungal enzyme. MAO-N has the C-terminal tripeptide Ala-Arg-Leu, which corresponds to the consensus targeting sequence found in many peroxisomal enzymes. The full-length cDNA for MAO-N was expressed in Escherichia coli from the T7 promoter of the expression vector pET3a, yielding a soluble and fully active enzyme form.

Amino Acid Sequence↗

PubMed1977

[Monoamine oxidase type B and the function of Ca2+, Mg2+-dependent adenosine triphosphatase of preparations of sarcoplasmic reticulum vesicles].

Oxidative deamination by monoamine oxidases of B type in the preparations of sarcoplasmic reticulum vesicles from rabbit skeletal muscles of beta-phenylethylamine or benzylamine was accompanied by a decrease of both the active transport of Ca2+ into the vesicles and Ca2+, Mg2+-dependent ATP-ase activity. This decrease was prevented by pretreatment of the vesicles with deprenyl, a specific monoamine oxidase type B inhibitor. The aldehydes formed in the course of enzymatic deamination of the substrates of type B, monoamine oxidases, are considered as possible participants in the regulation of Ca2+, Mg2+-dependent ATP-ase activity.

Adenosine Triphosphatases↗

PubMed1996

Platelet phenolsulphotransferase activity, monoamine oxidase activity and peripheral-type benzodiazepine binding in demented patients.

Blood platelet phenolsulphotransferase and monoamine oxidase activities, as well as platelet peripheral-type benzodiazepine binding have been studied in several neuropsychiatric disorders, in order to identify biochemical markers for altered brain functioning. In the present work, we determined platelet phenolsulphotransferase and monoamine oxidase activities in demented patients: they showed significantly higher phenolsulphotransferase and monoamine oxidase activities than controls. A significant positive correlation was found between enzyme activities and severity of illness. In the same subjects, we evaluated platelet peripheral-type benzodiazepine binding: a significant reduction of Bmax values was observed in demented patients, whereas Kd values did not substantially differ between the two subject groups. These findings are discussed with reference to central nervous system biochemical abnormalities of demented subjects: it may be that in Dementia of Alzheimer type either some central biochemical changes are reflected in certain peripheral tissues (such as platelets), or a systemic derangement occurs together with a cerebral involvement.

Aged↗

PubMed1988

The involvement of intestinal monoamine oxidase in the transport and metabolism of tyramine.

The monoamine oxidase activities were found to be similar in the crypt and villous cells of the different regions of rat small intestine. In all cases the activity of the A-form of the enzyme constituted more than 70% of the total. A similar proportion of that form of the enzyme was found in homogenates of biopsy samples of human intestine. Studies with everted intestines showed that at concentrations above 10 microM over 70% of tyramine was deaminated during transport and the use of selective inhibitors confirmed the A-form of monoamine oxidase to play the dominant role in that process.

Animals↗

PubMed1977

Ultracytochemical demonstration of monoamine oxidase activity in nervous and non-nervous tissue of the rat.

A method is described for the ultrastructural localization of the enzyme monoamine oxidase based on the formation of an osmiophilic formazan from the tetrazolium salt (2-(2'-benzothiazolyl)-5-styrl-3-(4'-phthalhydrazidyl) tetrazolium chloride) (BSPT) and using tryptamine as substrate. It was tested in rat heart, liver, adrenal cortex and medulla, kidney, pineal gland, cerebral cortex and cerebellar cortex and was found to provide good ultrastructural preservation, high contrast of the specific, enzyme-dependent precipitate and improved sensitivity. Monoamine oxidase activity was found in the mitochondrial outer compartment, nuclear envelope and endoplasmic reticulum in all organs studied; it was also seen occasionally in plasma membranes of liver and heart. Similar localizations were observed in interstitial cells and capillary endothelial cells. The enzyme-dependent nature of the observed precipitate was verified by control experiments consisting of incubation of overfixed tissue, omission of substrate from the incubation medium, and incubation in the presence of a specific, nonreversible inhibitor, pargyline. These studies confirm and extend the results of cell fractionation studies using liver, demonstrate the widespread distribution of monoamine oxidase in tissues, and suggest that monoamine oxidase plays important functional roles in extraneuronal cells.

Adrenal Glands↗

PubMed1976

Towards rational therapy with monoamine oxidase inhibitors.

A rational approach to the use of monoamine oxidase inhibitors (MAOIs) is outlined. Patients suitable for treatment cannot be classified adequately using conventional diagnostic labels. They include those with primary symptoms of hypochondriasis, agoraphobia and social phobias, irritability, somatic anxiety and anergia; those with primary depressed mood, guilt, ideas of reference and personality disorders seldom respond. There is great variation in the interval between the first administration of these drugs and clinical response, and this may account for the inconsistencies in published trials. The type of drug and its dose may affect rate of response, as may biochemical factors, including acetylator and monoamine oxidase status. To obtain maximum benefit, a course of therapy with MAOIs should last for several months.

Adjustment Disorders↗

PubMed1985

Reversible inhibition and mechanism-based irreversible inactivation of monoamine oxidases by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP).

It has been suggested (Chiba et al., Biochem. Biophys. Res. Communs. (1984) 120, 574) that the neurotoxic effects of MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine), which causes Parkinsonian symptoms in humans and other primates, are due to compounds resulting from the oxidation of MPTP by monoamine oxidase B in the brain. We reported recently that both monoamine oxidase A and B oxidize MPTP to MPDP+, the 2,3-dihydropyridinium form and that the reaction is accompanied by time-dependent, irreversible inactivation of the enzymes. Of the two forms of monoamine oxidase, the B enzyme oxidizes MPTP more rapidly and is also more sensitive to inactivation. We now wish to report that MPTP, as well as its oxidation products, MPDP+ and MPP+, the 4-phenylpyridinium form, are also potent reversible, competitive inhibitors of both monoamine oxidase A and B, particularly the former, and that the order of inhibition for the A enzyme is MPDP+ greater than MPP+ greater than MPTP, while for the B enzyme MPTP greater than MPDP+ greater than MPP+. We further report on the spectral changes and isotope incorporation accompanying the irreversible inactivation.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

PubMed1984

Inhibition of brain monoamine oxidase by 1,2,4-trisubstituted 5-imidazolones.

Nine 1-(3,4-dimethoxyphenethyl)-2-methyl-4-(substituted benzylidene)-5- imidazolones were evaluated for their ability to inhibit the activity of rat brain monoamine oxidase during oxidative deamination of tyramine, 5-hydroxytryptamine (serotonin), and kynuramine. All substituted imidazolones inhibited monoamine oxidase activity. A concentration-dependent inhibition of monoamine oxidase was observed using kynuramine as the substrate and the degree of enzyme inhibition was also evaluated on the basis of their I50 values. Preincubation of imidazolones with the enzyme preparations for varying lengths of time prior to the addition of substrate in no way altered their degree of inhibition and thus exhibited a reversible nature of inhibition. A kinetic study carried out with 1-(3,4-dimethoxy-phenethyl)-2-methyl-4-(4- nitrobenzylidene )-5- i midazolone revealed a competitive nature of inhibition of rat brain monoamine oxidase.

Animals↗

PubMedDate not supplied

[Spectrophotometric method of determining monoamine oxidase activity in human thrombocytes].

A method for estimation of monoamine oxidase activity in human thrombocytes is developed. The method is based on coupling of monoamine oxidase and alcohol dehydrogenase reactions. The method was highly reproducible. Small volumes of blood were required for analysis. Values of MAO activity, obtained by the method, were in good agrement with the data published in literature.

Blood Platelets↗

PubMed1980

p-Methoxyamphetamine, a potent reversible inhibitor of type-A monoamine oxidase in vitro and in vivo.

p-Methoxyamphetamine is over 20 times as potent as (+)-amphetamine as an inhibitor of 5-HT oxidation by monoamine oxidase in mouse brain in vitro, with a Ki value of 0.22 microM. It is highly selective towards A-type monoamine oxidase and possesses only weak activity against the B-type enzyme (Ki value about 500 microM with benzylamine as substrate and solubilized rat liver mitochondria as enzyme source). It is 10 times more active than (+)-amphetamine in protecting mouse brain monoamine oxidase from inhibition by phenelzine in vivo. o-Methoxy- and m-methoxyamphetamines inhibit monoamine oxidase both in vitro and in vivo with potencies comparable with, or less than that of (+)-amphetamine.

Amphetamine↗

PubMed1984

A simple assay for monoamine oxidase using glutathione peroxidase and glutathione reductase.

A new fluorometric assay for the determination of monoamine oxidase activity that is applicable to any substrates including dopamine and serotonin is described. Hydrogen peroxide formed during the monoamine oxidase reaction was reduced in the presence of glutathione and glutathione peroxidase, and the oxidized glutathione was measured fluorometrically as NADP+ via oxidation of NADPH by glutathione reductase. This method was applied for inhibitor studies using clorgyline and deprenyl.

Animals↗

PubMedDate not supplied

[Monoamine oxidase activity of rat brain under cold exposure].

Cold stress and cold adaptation were studied for their effect on the activity and substrate specificity of the monoamine oxidase A and B and on the Km of serotonin deamination in the rat brain mitochondria and supernatant. Mitochondrial monoamine oxidase Km with serotonin is established to increase more than twice under cold stress and decrease considerably in cold adapted rats. The lowering of the mitochondrial monoamine oxidase A activity is accompanied by the appearance of serotonin and the glucosamine deaminating activity in supernatant. The data suggest that decrease in the monoamine oxidase activity under cold stress may be caused by both release of the enzyme from mitochondrial membrane and changes in its catalytic property alteration.

Adaptation, Physiological↗

PubMed2003

Monoamine oxidase and cigarette smoking.

Current cigarette smokers have reduced monoamine oxidase (MAO) and there is evidence that this is a pharmacological effect of tobacco smoke exposure rather than a biological characteristic of smokers. This article summarizes human and animal studies documenting the inhibitory effects of tobacco smoke on MAO and discusses MAO inhibition in the context of smoking epidemiology, MAO inhibitor compounds in tobacco, reinvestigations of low platelet MAO in psychiatric disorders and smoking cessation.

Animals↗

PubMed1979

[Kinetic patterns of their reactions catalyzed by membrane-bound monoamine oxidase].

The initial rate (v) versus initial substrate concentration [S]0 plots for the reaction of serotonin deamination catalyzed by rat liver mitochondrial monoamine oxidase are characterized by complicated non-hyperbolic patterns. The shapes of the curves in the plots depend on the age and strain of the animals used or on alterations in the physico-chemical state of mitochondria caused by freezing -- thawing and swelling in hypotonic solutions. The v versus [S]0 plots for other substrates (e. g. tyramine) do not obey the Michaelis -- Menten equation as well. In order to interpret the kinetic patterns described a model of the mitochondrial monoamine oxidase structure and function has been proposed. The model is based on the assumption that both catalytic and regulatory allosteric sites are present on the surface of monoamine oxidase molecules. In the process of serotonin or tyramine binding the monoamine oxidases exhibit cooperative properties which are characteristic for the allosteric enzymes. The model also suggests an active regulatory role of the mitochondrial membrane itself.

Animals↗

PubMed1994

Confluentic acid and 2'-O-methylperlatolic acid, monoamine oxidase B inhibitors in a Brazilian plant, Himatanthus sucuuba.

Monoamine oxidase B (MAO-B) inhibitors were isolated from the bark of a Brazilian plant, Himatanthus sucuuba (SPR.). Assignments of the 1H- and 13C-NMR data using two dimensional (2D)-NMR techniques showed the active components to be known lichen depsides, confluentic acid (1) and 2'-O-methylperlatolic acid (2). The depside (1) showed selective inhibition of MAO-B with IC50 value of 0.22 microM.

Animals↗

PubMed1975

The nature of inhibition of cat brain mitochondrial monoamine oxidase by clorgyline.

In the cat brain the highest monoamine oxidase (MAO) activity is observed in the hypothalamus followed by hippocampus, caudate nucleus, pons and median cortex. Tyramine was the most actively deaminated substrate tested followed by dopamine. Clorgyline was more selective in its inhibitory action and could distinguish between tyramine and dopamine MAO deaminating system. The latter being more resistant to inhibition. The multiple forms of solubilized MAO as separated by polyacrylamide gel electrophoresis have varying phospholipid phosphorus content and sensitivity to inhibition by clorgyline in vitro and in vivo.

Animals↗