Reactivity of liver monoamine oxidase in the seal Phoca hispida ladogensis

The goal of this work consisted in substrate and inhibitor specificity of liver monoamine oxidase (MAO) of the freshwater Ladoga subspecies of the ringed seal Phoca hispida ladogensis. The studied enzyme has been found to have the large substrate specificity by deaminating, apart from eight classic substrates of the terrestrial mammalian MAO, also histamine, the substrate of diamino oxidase. It has been revealed that the studied enzyme realizes wide substrate specificity by deaminating, apart from eight classic MAO substrates of terrestrial mammals, also histamine, the substrate of diamino oxidase. The deamination rates of benzylamine, β-phenylethylamine, and N-methylhistamine are found to be almost by one order higher than the deamination rates of serotonin and noradrenaline. The seal liver MAO did not deaminate putrescine and cadaverine and was insensitive to 10^?2 M semicarbaside. There were calculated bimolecular rate constants of interaction of inhibitors: chlorgyline, deprenyl, berberine, sanguinarine, chelidonine, and four derivatives of acridine with the enzyme at deamination of nine substrates. By the method of substrate-inhibitor analysis we have shown heterogeneity of the enzyme, i.e., the presence in the seal liver of at least of two different MAO.     

Comparative study of catalytic properties of mink and rat liver monoamine oxidase

Comparative substrate-inhibitor analysis of catalytic properties of mitochondrial monoamine oxidase (MAO) of liver of the American mink Mustela vison Schreber and of liver of Wistar rat has been performed. It has been found that MAO of mink, like MAO of rat, has properties of classic mammalian MAO: it deaminates tyramine, tryptamine, serotonin, benzylamine, β-phenylethylamine and does not deaminate histamine as well as does not have sensitivity to semicarbazide. Study of kinetics of the monoamine oxidase deamination revealed both qualitative and quantitative differences between these enzymes. Specificity of action on MAO-A form of four irreversible inhibitors—acridine derivatives—has been shown; this specificity was several times higher for the mink liver MAO than for the rat liver MAO. It is suggested that the liver MAO of both species of the studied animals has several isoenzyme forms or several centers of the substrate binding.     

Comparative enzymological study of catalytic properties of liver monoamine oxidases in frogs

Comparative enzymological study of catalytical properties of monoamine oxidase (MAO) of liver of the marsh frog Rana ridibunda and common frog Rana temporaria has revealed certain features of similarity and differences between these enzymes. The MAOs from both studied biological sources show catalytic properties resembling those of the classical MAO of terrestrial vertebrates: they deaminate tyramine, tryptamine, serotonin, and benzylamine and do not deaminate histamine, have sensitivity to clorgyline, the specific inhibitor of the MAO A form, and deprenyl, the specific inhibitor of the MAO B form, and are not inhibited by 10⁻² M semicarbazide. Based on data of substrate-inhibitor analysis, a suggestion is put forward about the existence of two molecular forms of the enzyme in liver of the studied frog species. Quantitative interspecies differences have been revealed between liver MAO of Rana ridibunda and Rana temporaria in values of kinetic parameters of reactions of deamination of several substrates and in sensitivity to the inhibitors, deprenyl and clorgyline. In the species Rana temporaria the MAO activity in reaction of deamination of serotonin and benzylamine were virtually identical, whereas in the species Rana ridibunda these parameters for serotonin were almost one order higher than for benzylamine. In the species Rana ridibunda, selectivity of action of deprenyl was expressed many times weaker, while selectivity of the clorgyline—one order of magnitude stronger than in the species Rana temporaria. The catalytic activities towards all studied substrates of liver MAO of both studied amphibian species were several times lower as compared with the enzyme of rat liver.     

Enzymologic characteristics of monoamine oxidase from liver of the skipjack tuna Katsuwonus pelamis

Substrate and inhibitory specificity of mitochondrial monoamine oxidase (MAO) from liver of skipjack tuna Katsuwonus pelamis was studied. The results of substrate—inhibitory analysis with application of chlorgilin and deprenyl might be indirect proofs of existence of one molecular MAO form in the tuna liver. Studied enzyme, as liver MAO of terrestrial mammals, deaminates tyramine, tryptamine, dopamine, serotonin, noradrenalin, benzylamine, β-phenylethylamine, N-methylhistamine and does not deaminate histamine, is not suppressed by 10 mM semicarbazide. Takrin, acriflavin, proflavin, acridine orange and pyronine G were established to be irreversible inhibitors of middle strength in respect to MAO of tuna liver. The specificity of inhibitors action upon deamination of various substrates was equal.     

Comparative enzymologic study of catalytical properties of liver monoamine oxidases of sturgeon fish

We carried out the comparative study of the substrate and inhibitory specificity of liver monoamine oxidases (MAO) of the giant sturgeon Huso huso, the starred sturgeon Acipenser stellatus, the Persian sturgeon Acipenser persicus, and the Russian sturgeon Acipenser gueldenstaedtii. Results of the substrate-inhibitor analysis with use of inhibitors chlorgilin and deprenil, as well as five specific substrates indicate homogeneity of these enzymes. All studied MAO have the several orders higher sensitivity to chlorgilin than to deprenil, with essential interspecies differences being observed. There are determined kinetic parameters of enzymatic deamination (K _M and V) of tyramine, serotonin, noradrenalin, benzylamine, β-phenylethylamine, and N-methylhistamine. All studied enzymes have been established to have the higher activity toward serotonin and noradrenalin-substrates of the MAO A form as compared with benzylamine, β-phenylethylamine, and N-methylhistamine-substrate of the mammalian MAO B form, the maximal activity being characteristic of the giant sturgeon.     

Comparative substrate-inhibitor analysis of mink liver monoamine oxidases

Comparative substrate-inhibitor analysis of catalytic properties of liver monoamine oxidases (MAO) was performed in the mature males of the American mink Mustela vison and the European mink Mustela lutreola. The action on the MAO activity was studied of alkaloids of the benzo[c]phenanthridine group: sanguinarine and chelidonine, diisoquinoline alkaloid berberine, medicinal agents “Ukrain” and “Sanguirythrin” as well as derivatives of 2-propylamine: deprenyl and chlorgylin. The latter turned out to be irreversible inhibitor of the MAO A form, whereas deprenyl-irreversible inhibitor of the MAO B form in both studied mink species. The selectivity of action of each inhibitor on the corresponding liver MAO form for the species M. vison was one order of magnitude stronger than for the species M. lutreola. All studied alkaloids as well medicinal agents on their basis have been shown to be specific irreversible inhibitors of the intermediate strength of the liver MAO A form of both mink species. They inhibit the enzymatic deamination of serotonin, tyramine, and tryptamine without affecting the deamination reaction of benzylamine and β-phenylethylamine (at concentrations of 10 mM and lower). Out of five studied isoquinoline agents, the medication “Ukrain” and alkaloid chelidonine have the highest inhibitory action; the agent “Sanguirythrin” and alkaloids berberine and sanguinarine produce the weaker monoamine oxidase effect. The revealed specificity of action of the studied inhibitors is an indirect evidence for the presence in the liver enzymes of both mink species, like in the rat liver enzyme, of several molecular forms.     

Comparative substrate-inhibitor analysis of liver monoamine oxidases of minks

Comparative substrate-inhibitor analysis of catalytic properties of liver monoamine oxidases (MAO) was performed in the mature males of the American mink Mustela vison and the European mink Mustela lutreola. The action on the MAO activity was studied of alkaloids of the benzo[c]phenanthridine group: sanguinarine and chelidonine, diisoquinoline alkaloid berberine, medication agents Ukrain and Sanguirythrin as well as derivatives of 2-propylamine: deprenyl and clorgylin. The latter turned out to be irreversible inhibitor of the MAO A form, whereas deprehyl--irreversible inhibitor of the MAO B form in both studied mink species. The selectivity of action of each inhibitor on the corresponding liver MAO form for the species M. vison was one order of magnitude stronger than for the species M. lutreola. All studied alkaloids as well medication agents on their basis have been shown to be specific irreversible inhibitors of the intermediate strength of the liver MAO A form of both mink species. They inhibit the enzymatic deamination of serotonin, tyramine, and tryptamine without affecting the deamination reaction of benzylamine and beta-phenylethylamine (at concentrations of 10 mM and lower). Out of the studied five isoquinoline agents, the medication Ukrain and alkaloid chelidonine have the highest inhibitory action; the agent Sanguirythrin and alkaloids berberine and sanguinarine produce the weaker monoamine oxidase effect. The revealed specificity of action of the studied inhibitors is an indirect evidence for the presence in the liver enzymes of both mink species, like in the rat liver enzyme, of several molecular forms.     

Comparative Study of Catalytic Properties of Monoamine Oxidases of the Liver of the Squid Todarodes pacificus and of the Liver of the Wistar Rat

A comparative study of substrate specificity of monoamine oxidase (MAO) in mitochondria of liver of the Pacific squid Todarodes pacificus and of Wistar rats is carried out. It is revealed that the squid liver MAO, unlike the rat liver MAO, is capable of deaminating not only tyramine, serotonin, and benzylamine, but also histamine. The squid liver MAO activity in relation to all studied substrates is approximately 10 times lower, while the sorption ability, several tens times lower, than the rat liver MAO. Semicarbazide, a classic inhibitor of diamine oxidase, at a concentration 1 × 10^–2 M did not inhibit the catalytic activity of both studied enzymes. The specificity of action of an irreversible inhibitor, proflavine, is established, which was seen at deamination of various substrates by the squid liver MAO to the greater degree, than by the rat liver MAO. The values of the bimolecular rate constant of the irreversible inhibition (k _II) by proflavine were 2.5–20-fold higher (depending on substrate) in the case of the squid liver MAO, than of the rat liver MAO. A suggestion is put forward about the probable presence of several centers of substrate binding in the enzyme of the studied marine invertebrate, like in the mammalian enzyme.     

Substrate-inhibitory analysis of monoamine oxidase from hepatopancreas of the octopus <Emphasis Type="Italic">Bathypolypus arcticus</Emphasis>

Study of the substrate-inhibitory specificity of mitochondrial monoamine oxidase (MAO) of hepatopancreas of the octopus Bathypolypus arcticus revealed distinctive peculiarities of catalytic properties of this enzyme. The studied enzyme, on one hand, like the classic MAO of homoiothermal animals, is able to deaminate tyramine, serotonin, benzylamine, tryptamine, b-phenylethylamine, while, on the other hand, it deaminates histamine and does not deaminate putrescine-classic substrates of diamine oxidase (DAO). Results of the substrate-inhibitory analysis with use of chlorgiline and deprenyl are indirect proofs for the existence in the octopus hepatopancreas of one molecular MAO form. Semicarbazide and pyronine G turned out to be weak irreversible inhibitors, four derivatives of acridine-irreversible inhibitors of the intermediate effectiveness with respect to the octopus hepatopancreas MAO; specificity of action of inhibitors at deamination of different substrates was equal.     

Catalytical properties of liver monoamine oxidases of the Commander squid <Emphasis Type="Italic">Berryteuthis magister</Emphasis> from various habitation zones

There has been performed kinetic analysis of enzymatic reactions of deamination of tyramine, tryptamine, serotonin, benzylamine, β-phenylethylamine, and histamine under action of liver monoamine oxidase (MAO) of the Commander squid Berryteuthis magister from various habitation zones in the Bering and Japan Seas. A substrate inhibition by high concentrations of all studied substrates has been revealed, which seems to indicate mutual effect of various MAO forms present in liver of the studied squids. Analysis of kinetic parameters of enzymatic reactions of deamination of six studied substrates and the substrate-inhibitory analysis with use of two derivatives of acridine and deprenyl indicate the enzyme heterogeneity, the presence of at least two MAO-A forms, and the absence of intraspecies differences in MAO of the Commander squids from various habitation zones. The most active was the MAO form responsible for serotonin deamination. There were obtained quantitative difference in substrate specificity and reaction ability with respect to inhibitor of proflavin for the liver MAO of the Commander and Pacific squids.     

Catalytic characteristics of monoamine oxidase of whitefish <Emphasis Type="Italic">Coregonus lavaretus ludoga</Emphasis>

Study of substrate-inhibitory specificity of liver mitochondrial monoamine oxidase (MAO) of adult individuals of the whitefish Coregonus lavaretus ludoga P. from the Ladoga Lake has revealed distinguished peculiarities of catalytic properties of this enzyme. The studied MAO, on one hand, like the classical enzyme of homoiothermal animals, is able to deaminate tyramine, serotonin, benzylamine, tryptamine, and β-phenylalanine, but, on the other hand, to deaminate histamine, the classic substrate of diamine oxidase. The found equal activity and sorptional ability of the enzyme toward six studied substrates including histamine, as well as results of the substrate-inhibitory analysis with use of specific inhibitors-deprenyl and chlorgilin-indicate homogeneity of the enzyme. The detected for the first time among the fish MAO wide substrate specificity and an unusually low sensitivity to both studied acetylene inhibitors does not allow ascribing unanimously the studied enzyme to the MAO forms known in organs and tissues of homoiothermal organisms. Apparently, the revealed enzyme form of this poikilothermal organism is not the true MAO, but performs a large amine oxidase function.     

Substrate-dependent activation energy of the reaction catalyzed by monoamine oxidase

The effect of temperature on the deamination of 5-hydroxytryptamine, tyramine, and phenethylamine by monoamine oxidase (MAO) of human placenta, beef liver, and rat liver has been studied. Both MAO A and MAO B activities are influenced by the lipid-phase transition and, in some cases, another type of transition. The estimates of activation energy (E_act) for the deamination of 5-hydroxytryptamine, phenethylamine, tyramine, dopamine, and pentylamine at 5–20 °C show that a given substrate is associated with a particular value irrespective of the source of MAO acting upon it. The substrate dependence of E_act is explained by the differences in lipophilicity of the various substrates. The interaction of enzyme and the lipids in the environment of its active site would differ with each substrate, and would give rise to different activated complexes, each corresponding to a given substrate. The E_act values are presumably related to these complexes, rather than to enzyme alone.     

Specificity of endogenous substrates for types A and B monoamine oxidase in rat striatum

Abstract: Studies were designed to evaluate specificity of the transmitter amines serotonin (5-hydroxytryptamine, 5-HT) and dopamine (DA), as well as the trace amines p -tyramine ( p -TA) and β -phenylethylamine (PEA) for types A and B monoamine oxidase (MAO) in rat striatum. 5-HT was found to be a specific substrate for the type A enzyme. However, the specificity of PEA for the type B enzyme was found to be concentration-dependent. When low concentrations of PEA and 5-HT were used to measure type B and type A activities, respectively, both clorgyline and deprenyl were highly selective for the sensitive form of MAO in vivo. However, as the concentration of PEA was increased, the type B inhibitor deprenyl became less effective in preventing deamination of PEA. Conversely, the type A inhibitor clorgyline became more effective in this regard. Kinetic analysis following selective in vivo inhibition showed PEA deamination by both forms of MAO with a 13-fold greater affinity for the type B enzyme. In vivo dose-response curves obtained with the common substrates DA and p -TA showed approximately 20% deamination by the B enzyme. Kinetic values for DA and p -TA deamination in in vivo -treated tissue possessing only type A or type B MAO activity, revealed a 2.5-fold greater affinity for the type A enzyme. These studies show the importance of concentration on substrate specificity in striatal tissue. The results obtained characterize the common substrate properties of DA and p -TA as well as of PEA in rat striatum. In addition, the presence of regional specificity for 5-HT deamination by only type A MAO is demonstrated.     

Monoamine oxidase activity in hepatopancreas of Octopus vulgaris

1. Monoamine oxidase activity has been studied in hepatopancreas of Octopus vulgaris using 5-HT and PEA as substrates.2. Time courses of MAO activity against 5-HT and PEA show that the enzyme has higher affinity for PEA than for 5-HT.3. MAO activity against 5-HT appears more sensitive than MAO activity against PEA, to variations of the temperature (range 17–67°C).4. The inhibition curves obtained with clorgyline and deprenyl indicate that MAO activity is due to a single form of the enzyme, not corresponding to type A and type B MAO.5. Semicarbazide 10⁻⁴ M does not affect the deamination of 5-HT and PEA, demonstrating that a semicarbazide-sensitive amine oxidase is not involved in this process.     

Catalytic characteristics of monoamine oxidase of whitefish Coregonus lavaretus ludoga

Study of substrate-inhibitory specificity of liver mitochondrial monoamine oxidase (MAO) of sexually mature individuals of the whitefish Coregonus lavaretus ludoga P. from the Ladoga Lake has revealed distinguished peculiarities of catalytical properties of this enzyme. The studied MAO, on one hand, like the classical enzyme of homoiothermal animals, is able to deaminate tyramine, serotonin, benzylamine, tryptamine, and beta-phenylalanine, but, on the other hand, to deaminate histamine, the classic substrate of diamine oxidase. The found equal activity and sorptional ability of the enzyme toward six studied substrates including histamine, as well as results of the substrate-inhibitory analysis with use of specific inhibitors--deprenyl and chlorgilin--indicate homogeneity of the enzyme. The detected for the first time among the fish MAO wide substrate specificity and an unusually low sensitivity to both studied acetylene inhibitors does not allow ascribing unanimously the studied enzyme to the known MAO forms of organs and tissues of homoiothermal organisms. Apparently, the revealed enzyme form of poikilothermal organism is not the true MAO, but performs a large amine oxidase function.     

Monoamine Oxidase Activity in the Hepatopancreas of the Kamchatka Crab <Emphasis Type="Italic">Paralithodes camtschaticus</Emphasis>: a Substrate–Inhibitor Specificity

A study of substrate–inhibitor specificity of mitochondrial monoamine oxidase (MAO) in the hepatopancreas of the adult Kamchatka crab Paralithodes camtschaticus revealed specific catalytic properties of the enzyme. On the one hand, crab hepatopancreas MAO, like its classical hepatic counterpart, can deaminate tyramine, tryptamine, dopamine, serotonin, noradrenalin, benzylamine, β-phenylethylamine and N-methylhistamine but shows no sensitivity to 10 mM semicarbazide. On the other hand, MAO deaminates histamine but not putrescine, two classical diamine oxidase (DAO) substrates. It was established that MAO activity was several times higher toward benzylamine, β-phenylethylamine and N-methylhistamine than toward serotonin and noradrenalin. MAO was also found to be almost 500 times more sensitive to its selective inhibitor deprenyl than to chlorogilyn. A substrate–inhibitory analysis with the use of deprenyl and chloroginyl provides an indirect evidence for the existence of a sole MAO molecular form in the Kamchatka crab hepatopancreas.     

Comparative study of inhibitory specificity of liver monoamine oxidase in frogs <Emphasis Type="Italic">Rana ridibunda</Emphasis> and <Emphasis Type="Italic">Rana temporaria</Emphasis>

A comparative enzymological investigation of inhibitory specificity of the liver monoamine oxidases (MAO) from the two frog species, lake frog Rana ridibunda and grass frog Rana temporaria, revealed certain interspecies similarities and distinctions of this enzyme. The anti-monoamine oxidase effect of five derivatives of acridine, three derivatives of phenothiazine and one derivative of xanthene (pyronine G) was comparatively analyzed. The tested six-membered tricyclic compounds were shown to exert an irreversible inhibitory effect on the enzyme from both biological sources, displaying the same substrate deamination specificity. Thus, the rate of interaction of acridine and phenothiazine derivatives with the MAO active center in both frog species was considerably higher when activity was determined using noradrenaline versus N-methylhistamine, while that of pyronine G—when activity was determined using N-methylhistamine versus noradrenaline. Interspecies quantitative differences were found in the inhibitory efficacy and degree of selectivity of the tested tricyclic compounds, indicative of the differences in catalytic properties of liver MAO at the interspecies level in the representatives of the genus Rana, family Ranidae. The data of substratespecific inhibitory analysis provide indirect evidence of the existence of two molecular MAO forms in the liver of the studied frog species.     

Comparative study of substrate and inhibitory specificity of monoamine oxidase of squid optic ganglia

Comparative study of substrate specificity of monoamine oxidase (MAO) of optic ganglia of the Pacific squid Todarodes pacificus and the Commander squid Berryteuthis magister has been carried out. The enzyme of the Pacific squid, unlike that of the Commander squid, has been established to be able to deaminate not only tyramine, tryptamine, serotonin, benzylamine, and β-phenylethylamine, but also histamine-substrate of diamine oxidase (DAO). In relation to all studied substrates, the MAO activity of optic ganglia of T. pacificus is several times higher as compared with that of B. magister. In the case of deamination of serotonin this difference was the highest and amounted to 5 times. Semicarbazide, the classic DAO inhibitor, at a concentration of 10 mM did not inhibit catalytic activity of both studied enzymes. The substrate-inhibitory analysis with use of deprenyl and clorgyline, specific inhibitors of different MAO forms, indicates homogeneity of the enzyme of the Pacific squid and heterogeneity of the Commander squid enzyme whose composition seems to contain at least two MAO forms. There are obtained quantitative differences in substrate specificity and reaction capability with respect to the inhibitors clorgylin and deprenyl for MAO of optic ganglia of the studied squid species. These differences probably can be explained by significant differences in the evolutionary level of these biological species.     

Phenylethanolamine is a specific substrate for type B monoamine oxidase

The characteristics of phenylethanolamine as both a competitive inhibitor and as a substrate for monoamine oxidase (MAO) were studied using rat brain and liver homogenates. Although phenylethanolamine, even at high concentrations (1 mM), produced minimal inhibition of MAO when serotonin (a substrate for type A MAO) was used as the substrate, it was a potent competitive inhibitor (K_i=11 μM) of the deamination of phenylethylamine (a substrate for type B MAO). When phenylethanolamine was used as a substrate, deprenyl, a selective inhibitor of type B MAO, was found to produce a single sigmoid inhibition curve at low concentrations of the inhibitor (pI₅₀=7.5). These results indicate that phenylethanolamine is a specific substrate for type B MAO. Identification of the products formed under the assay conditions show that phenylethanolamine is converted to both mandelic acid and phenylethylene glycol by liver homogenates but only to the latter, neutral metabolite by brain homogenates.     

Deamination of Aliphatic Amines by Monoamine Oxidase A and B Studied Using a Bioluminescence Technique

Deamination of n-octylamine and n-decylamine has been studied in various tissues using a new bioluminescence technique. Selectivity of n-octylamine and n-decylamine as substrates for monoamine oxidase (MAO) A or B has been determined using both clorgyline and (-)-deprenyl inhibition curves and kinetic parameters. Homogenates of rat brain, liver and heart containing predominantly MAO-A or -B were prepared by preincubation for 60 min with (-)-deprenyl or clorgyline (30 nM), respectively. Human placenta (MAO-A) and platelet (MAO-B) were used as reference tissues containing only one MAO form. In tissues (rat liver, brain) containing both MAO forms in equal proportion, inhibition curve studies showed a preference of both substrates for the B form of the enzyme; however, where MAO-A was the major form (rat heart, human placenta), clorgyline was the more effective inhibitor. In the beef brain cortex n-octylamine showed marked preference for MAO-B, whereas n-decylamine was selective toward-MAO-A. Kinetic studies in general supported the picture of greater selectivity of the aliphatic amine substrates for deamination by MAO-B, as reflected by lower Km values for this enzyme type. However, n-octylamine was more selective for MAO-B than n-decylamine in both kinetic and inhibition curve studies. The deamination of these aliphatic amine substrates cannot be explained only by reference to the binary classification of MAO into types A and B.