Monoamine Oxidase Reaction Research Articles

Oxygen dependency of monoamine oxidase activity in the intact lung.

Hydrogen peroxide generated by monoamine oxidase (MAO)-mediated deamination of biogenic amines has been implicated in cell signaling and oxidative injury. Because the pulmonary endothelium is a site of metabolism of monoamines present in the venous return, this brings into question a role for MAO in hyperoxic lung injury. The objective of this study was to evaluate the O(2) dependency of the MAO reaction in the lung. To this end, we measured the pulmonary venous effluent concentrations of the MAO substrate [(14)C]phenylethylamine and its metabolite [(14)C]phenylacetic acid after the bolus injection of either phenylethylamine or phenylacetic acid into the pulmonary artery of perfused rabbit lungs over a range of PO(2) values from 16 to 518 Torr. The apparent Michaelis constant for O(2) was approximately 18 microM, which is more than an order of magnitude less that measured for purified MAO. The results suggest a minimal influence of high O(2) on MAO activity in the normal lung and demonstrate the importance of measuring reaction kinetics in the intact organ.

Biochemical and functional changes during the bovine fetal thyroid development.

To establish biochemical and functional relations during thyroid development, the activity of thyroid peroxidase (TPO), nicotinamide adenine dinucleotide phosphate (NADPH)-cytochrome c reductase and monoamine oxidase (MAO) in a particulate fraction and the iodide transport and organification in slices of bovine fetal thyroid were examined throughout gestation. The cytochemical localization of TPO, H2O2 generating sites and MAO was also studied. Fetal glands were grouped in stages I to V according to increasing developmental features; adult tissues were also analyzed. TPO activity in each of the fetal stages was higher than in the adult; a marked increase was observed in stages IV and V. Iodide transport (T/M) was similar in stages I to V and the adult. Iodide organification in fetal thyroids showed a similar pattern to that of TPO activity. When compared with the adult, at midgestation (stages II to III), a lower iodination coexisted with a higher TPO activity. The activity of NADPH-cytochrome c reductase and MAO, two enzymes previously proposed to participate in thyroid H2O2 generation, did not parallel the level of iodide organification. Cells from stages II to V exhibited a positive cytochemical reaction for TPO in the rough endoplasmic reticulum (RER) and the perinuclear cisternae (PC). In stages IV, V, and adult, TPO was occasionally found in apical vesicles and microvilli, whereas H2O2 was detected within the RER and the PC. MAO reaction was positive in adult, but not in fetal thyroid. These results indicate that a high TPO activity accompanied the onset of the organification process during fetal thyroid development. The level of iodination was associated with the presence of TPO at a proper site rather than to the level of TPO activity. Evidence against a role of NADPH-cytochrome c reductase and MAO in the iodide organification was obtained.

A discontinuous luminometric assay for monoamine oxidase

A simple, sensitive and convenient discontinuous luminometric assay for monoamine oxidase (MAO) is described. It is based on measurement of the light production from the peroxjdase-catalysed chemiluminescent oxidation of 5-amino-2,3-dihydro-1,4-phthalazinedione (luminol) by the hydrogen peroxide produced in the MAO reaction. The procedure is suitable for use with a wide range of MAO substrates, although 5-hydroxytryptamine, adrenaline and noradrenaline are too readily oxidized by hydrogen peroxide to be used. A particular advantage of this procedure is that it is applicable to the oxidation of substrates which do not yield products, such as an aldehyde or free ammonia, which form the basis of several alternative substrate-independent assay procedures. The application of the procedure to assay the oxidation of benzylamine, tyramine and 2- n-pentylaminoacetamide (milacemide) by a crude mitochondrial preparation from rat liver and purified ox liver MAO-B is demonstrated.

Histochemical detection of monoamine oxidase and alcohol dehydrogenase activities in the Syrian hamster Harderian glands: existence of a sexual dimorphism.

Monoamine oxidase (MAO) and alcohol dehydrogenase (AD) activities were studied histochemically in the Syrian hamster Harderian gland using tryptamine as substrate and Nitroblue Tetrazolium as the final electron acceptor. No dark: light-related changes were observed. Male type I secretory cells showed an intense MAO reaction. Female type I cells exhibited a moderate MAO activity. Both male and female glands showed a moderate/intense AD-positive reaction. Male type II cells were lacking MAO and AD activities. MAO activity found in the hamster Harderian glands corresponded mainly to MAO type A since treatment with chlorgyline (0.01, 0.1 and 0.5 mM) totally inhibited it. The possible role of these two enzymes in Harderian gland indolalkylamine metabolism is discussed.

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 using clorgyline and deprenyl.

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.

Histochemical studies on the distribution of hexokinase and several enzymes related to catecholamine production in the locus coeruleus of the squirrel monkey

Summary Detailed histochemical studies have been conducted on the distribution of hexokinase (HK), monoamine oxidase (MAO), L-gulonolactone oxidase (GO) and NAD-linked xylitol dehydrogenase (XY) in every component of the locus coeruleus (LC) of the healthy juvenile male squirrel monkey (Saimiri sciureus). In addition, the reactions of MAO and GO have been tested in the LC of the healthy adult male rat of the Wistar strain. In contrast with many other species of mammals whose LC is equally composed of both medium-sized neurons and small neurons, the LC of the squirrel monkey consists almost exclusively of medium-sized neurons. The LC was clearly discerned from the surrounding brain tissue by the HK reaction, because the neurons with relatively weak activity were embedded in the neuropil with moderate activity and surrounded by the glial cells with moderate to strong activity. The neurons of C4 revealed varying degrees of positive reactions. Most of its neurons exhibited moderate activity suggesting that these neurons may receive energy supplies indirectly from the glial cells; whereas a few neurons on its surface showed strong activity hinting that they may receive energy supplies directly from glucose in the circulating blood. The presence of both types of energy supplies in the LC may facilitate keeping a glycemie level constant in the respiratory center of the monkey. The perikarya of neurons were moderately to strongly positive while the blood capillaries were more strongly positive and some glial cells were strongly positive with regard to the MAO reaction. This gave the LC a marked coloration as a whole. It is suggested that so far as the squirrel monkey is concerned, active monoamine metabolism in an individual neuron of the LC may undergo phasic changes depending on the functional state of that cell. In LC, MAO may be concerned with inactivation of catecholamines rather than the general metabolism of an autonomic nucleus. Most of the neurons revealed varying degrees of positive activity for the GO test while some neurons showed much more positive granules than the others for the XY test. These results strongly suggest that there is a high possibility that at least some neurons of the LC may have the ability to synthesize vitamin C. This ability may be closely related to the catecholamine production, which is involved in the process of formation of neuromelanin, in the LC. In contrast to the squirrel monkey, the LC of the rat was devoid of GO and XY, although its liver showed strong GO activity. It is suggested that the LC is independent of the liver in regard to the ability to synthesize vitamin C in some species of mammals.

Effects of hydroxylamine on mitochondrial monoamine oxidase in rat liver.

The report here is the study as for the effects of NH2OH on the enzymic reaction of monoamine oxidase (MAO) using rat liver mitochondria. In the short-term reaction (1 min) by MAO, NH2OH decreased the MAO activity by either tyramine or benzylamine as substrate. In the long-term reaction (60 min), there was an increased activity in the MAO reaction by tyramine and an decreased one in that by benzylamine under various concentrations of NH2OH. In the long-term reaction, Km-values for tyramine and benzylamine were 1.82×10-3.0M and 2.50×10-2.0M, respectively, which were consistent with those in the presence of NH2OH. Pursuing the changes of MAO activities by various concentrations of NH2OH using the tyramine substrate at intervals of 1, 10, 30, and 60 min, there was a decrease of MAO activity accompanying an increased concentration of NH2OH after 1 min period, a partial increase after 10 min, and an entire increase in extensive concentrations of NH2OH after 30 min. In the other substrates such as tryptamine, amylamine, hexylamine, and β-phenylethylamine, the effects of NH2OH on MAO were similar to those in tyramine. In the butylamine substrate, NH2OH caused as inhibitory effects as shown in the benzylamine substrate. These results suggest the existence of a complex of MAO enzymes corresponding to monoamine substrates. The multiplicity of MAO enzyme is further discussed in the text.

Monoamine oxidase in the neurohypophysis of the newt (Cynops pyrrhogaster pyrrhogaster), the toad (Bufo bufo japonicus) and the tortoise (Clemmys japonica).

Distribution of monoamine oxidase (MAO) was histochemically determined in the neurohypophysis of the newt (Cynops pyrrhogaster pyrrhogaster), the toad (Bufo bufo japonicus), and the tortoise (Clemmys japonica) by means of a tryptamine-tetrazolium (TNBT) method. The median eminence in all of these species gave a similar MAO reaction. The ependymal cells showed a very slight or no MAO activity. MAO-positive fibers, which extended rostro-caudally to the pars nervosa, were observed in the fiber layer of the median eminence. In the external layer of the median eminence, a large number of strongly MAO-positive fibers were identified around blood capillaries of the primary portal plexus. In the tortoise, these fibers were more conspicuous in the posterior region of the median eminence than in its anterior region. The presence of MAO-positive fibers around the portal blood capillaries suggests that a monoaminergic mechanism is functional in the regulation of the secretion of releasing factors at the level of the median eminence. MAO-positive fibers in the pars nervosa were, like in the median eminence, thickly distributed around the blood capillaries. In the pars intermedia, there were a considerable number of MAO-positive fibers among the intermedia cells and sometimes in close contact with them. These fibers appeared to innervate the pars intermedia via the pars nervosa.

Histochemical mapping of the distribution of monoamine oxidase in the diencephalon and basal telencephalic centers of the brain of squirrel monkey ( Saimiri sciureus)

The activity of monoamine oxidase (MAO) was mapped at the macroscopic level using 50 μ thick fresh frozen sections arranged in a caudo-cranial series of sections through the diencephalon and basal telencephalic centers of the squirrel monkey brain. The various thalamic nuclei show a mild MAO reaction except the nuclei periventricularis and para- and subfascicularis, which show moderate MAO reaction. The hypothalamus, in general, shows a stronger MAO reaction than the thalamus, because of its involvement in various autonomic functions. The nuclei paraventricularis, supraopticus and ventromedialis hypothalami are particularly prominent because of the stronger MAO activity they show in contrast to other hypothalamic areas. The nucleus caudatus, putamen and globus pallidus show mild to moderate MAO activity. The fiber bundles of fimbria hippocampi, fornix, anterior commissure and internal capsule show a moderate to moderately strong MAO reaction. The nuclei of the amygdaloid complex differ little from one another and show negligible to mild MAO activity. The nuclei dorsalis, medialis and lateralis septi show a mild MAO reaction compared to the moderate activity in the nuclei fasciculi diagonalis Brocae and triangularis septi.

INTRACELLULAR MONOAMINE OXIDASE AND LIPIDS IN DIFFUSION CHAMBER CULTURES OF THE PINEAL ORGAN.

Outgrowth of rat pineal tissue in diffusion chambers began with a migration of connective tissue cells from the implant, and this was followed by a spreading of the parenchymal cells to the margins of the chambers. Diffusion chamber implants and fresh slices of pineal organ were incubated for monoamine oxidase (MAO) in a medium containing nitro-blue tetrazolium and tryptamine hydrochloride. The MAO reaction was visualized as black formazan granules in parenchymal cells of all cultures throughout the entire 21 day observation period. These cytoplasmic granules appeared to increase in number and in size during the later time periods. A positive enzyme reaction also was present in slices of fresh pineal organ treated in the same medium and in a medium without the substrate, tryptamine hydrochloride. Pineal tissues with prior treatment in a MAO inhibitor gave a negative reaction. Some parenchymal cells in diffusion chamber implants accumulated many large lipid droplets. There were fewer of these cells than MAO positive cells, and they appeared to migrate from the implant at a slower rate.

Concomitant analysis for oxygen uptake and ammonia evolution during the monoamine oxidase reaction

The use of the transfer rate of a volatile substance (ammonia) for the expeditious development of a method for quantitation of this substance during respirometric tests was discussed. A quantitative study of the conditions and details of the method were presented.