Properties Of Monoamine Oxidase Research Articles

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 lake frog Rana ridibunda and brown 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, benzylamine and do not deaminate histamine, have sensitivity to chlorgiline, the specific inhibitor of the MAO A form, and deprenyl, the specific inhibitor of the MAO B form, and are not inhibited with 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. Interspecies quantitative 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 practically identical, whereas in the species Rana ridibunda these parameters for serotonin were almost one order of magnitude higher than for benzylamine. For the species Rana ridibunda, selectivity of action of deprenyl was expressed many times weaker while selectivity of the chlorgiline--one order of magnitude stronger than for the species Rana temporaria. The catalytic activity for all studies substrates of liver MAO of both studied amphibian species were several times lower as compared with the enzyme of rat liver.

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

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

Catalytic properties of monoamine oxidase from mink (Mustela vison) liver

Catalytic properties of monoamine oxidase from mink (Mustela vison) liver

Catalytic properties of monoamine oxidase from the lamprey Lampetra fluviatilis liver

270 The substrate-inhibition specificity of liver monoamine oxidase (MAO) has been studied in mature lampreys ( Lampetra fluviatilis ) of both sexes. The catalytic properties of the enzyme have been found to resemble those of the classic mammalian MAO: the enzyme deaminates tyramine, tryptamine, serotonin, and benzylamine, but not histamine; it is sensitive to proflavin, the well-known type A MAO inhibitor; and is not inhibited by 10 ‐2 M semicarbazide. It is assumed that the MAO from the lamprey liver, as well as liver MAOs of other hydrobionts (squids and fish), has several substrate-binding sites or is represented by several isozymes. The observed specificity of the inhibitory effect of proflavin confirms this assumption. The detoxicating activity of the lamprey liver MAO is low, which may be accounted for by the anatomical and physiological characteristics of the digestive system of lampreys. The enzyme monoamine oxidase (monoamine:O 2 oxidoreductase (deaminating); EC 1.4.3.4) plays the key role in the adrenergic neurotransmitter metabolism and implements an important barrier function on inactivation of biogenic amines [1‐3]. Although this enzyme was discovered more than 80 years ago, its functional role remains obscure. It was established that, in the majority of animals, this enzyme is highly active in the liver and brain [1]. To date, the catalytic properties of liver MAO have been studied predominantly in representatives of higher terrestrial animals. In numerous representatives of the most ancient class of contemporaneous aquatic vertebrates, Cyclostomata, only the MAO from the lamprey Lampetra japonica brain [4] and the hagfish Eptatretus burgeri brain [5‐7] have been studied. Notably, the activity of lamprey liver MAO has not been studied earlier.

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 (kII) 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.

One amino acid residue cannot determine the differences in the catalytic and regulatory properties of monoamine oxidases A and B.

One amino acid residue cannot determine the differences in the catalytic and regulatory properties of monoamine oxidases A and B.

Properties of Monoamine Oxidase in Monkey Heart

The activities of monoamine oxidase (MAO) in a homogenate and the mitochondrial fraction of monkey (Macaca facicularis) heart were measured with labelled benzylamine, serotonin (5-HT), tyramine and β-phenylethylamine (PEA) as substrates. The effects of clorgyline, deprenyl and semicarbazide on MAO were also investigated. Benzylamine deamination was more sensitive to deprenyl than to clorgyline, although it was not completely inhibited by a high concentration of either, and the remaining activity was completely inhibited by pretreatment with semicarbazide. The activities of 5-HT and tyramine were both more sensitive to clorgyline than to deprenyl, and both inhibitors gave single-sigmoidal inhibition curves. Experiments with increasing concentrations of PEA as substrate and clorgyline and deprenyl as inhibitors indicated that at higher concentrations, PEA was a substrate for MAO-A as well as MAO-B in monkey heart. These results suggest that monkey heart mitochondria contain not only MAO-A and MAO-B, but also clorgyline resistant amine oxidase (CRAO). The ratio of MAO-A, MAO-B and CRAO was determined from plots of inhibitions with each substrate. The kinetic constants of MAO in monkey heart were compared with those of MAO in hearts of other an mals. The enzymic properties of MAO in monkey heart were discussed on the basis of these results.

Some properties of monoamine oxidase in carp heart

1. Studies using clorgyline, deprenyl and semicarbazide as inhibitors showed that carp heart homogenate contained a new type of monoamine oxidase (MAO) and a clorgyline- and deprenyl-resistant amine oxidase (CRAO). 2. The deamination of monoamines by carp heart MAO proceeded in two steps by a double- displacement (ping-pong) mechanism. 3. The K m values of the MAO for oxygen ( K 0 values) with tyramine, 5-hydroxytryptamine (5-HT) and β-phenylethylamine (PEA) as substrates were identical (59 μM).

Some properties of monoamine oxidase and a semicarbazide sensitive amine oxidase capable of the deamination of 5-hydroxytryptamine from porcine dental pulp

The deamination of 5-hydroxytryptamine, tryptamine and benzylamine by porcine dental pulp membrane preparations is brought about not only by monoamine oxidase, but also by a clorgyline (and deprenyl) resistant, semicarbazide sensitive enzyme. The semicarbazide sensitive enzyme was also inhibited by aminoguanidine, hydroxylamine and phenylhydrazine, but was not affected to any significant extent by incubation at 50° for up to 100 min. There was, on the other hand, considerable inhibition of monoamine oxidase activity after incubation at this temperature. The semicarbazide sensitive enzyme neither metabolised, nor was inhibited by putrescine or cadaverine. Mixed substrate experiments indicated that 5-hydroxytryptamine and tryptamine interacted at the same catalytic centre on the semicarbazide sensitive enzyme.

Monoamine oxidase activity in ox, elk and reindeer brains

1. 1. Some properties of monoamine oxidase (MAO) in the brains of ox, elk and reindeer have been investigated. 2. 2. The K m values towards 5-hydroxytryptamine, tyramine and β-ohenethylamine were similar for all three species, as were the substrate specificities (with respect to tyramine) of the enzyme towards 5-hydroxytryptamine, β-phenethylamine, tryptamine, adrenaline, norarenaline and kynuramine 3. 3. The absolute activity of MAO was lower in the elk and reindeer than in the ox. The activities of the enzymes succinate dehydrogenase, acid phosphatase and NAD +-nucleosidase, but not fumarase, were also lower in the elk and reindeer than in the ox. 4. 4. Experiments with the substrate-selective inhibator clorgyline indicated that both MAO-A and -B were present in all three tissues, but that the -A form of the enzyme was responsible for the bulk of the deamination of the substrates tested ( 5-hydroxytryptamine, tyramine and β-phenethylamine), particularly in the reindeer.

Properties of monoamine oxidase in control and Lesch-Nyhan fibroblasts.

Monoamine oxidase activity of the A type was measured in homogenates of cultured human skin fibroblasts. Twenty-four control lines had activities ranging over fifty-fold with an apparent bimodal distribution. Activity in fibroblasts from 20 patients with the Lesch-Nyhan syndrome fell in the low portion of the normal distribution with a mean activity about 50% that of the control mean (p < 0.05). In a subgroup of control and Lesch-Nyhan lines with levels of enzyme activity from 0.9 to 179 pmol/min/mg protein, monoamine oxidase was similar with respect to apparent Km for tryptamine, thermal stability at 56 C, and sensitivity to clorgyline. Thus the lower mean levels of activity observed in the Lesch-Nyhan as compared to control fibroblasts were not associated with other altered properties of the enzyme. The bimodal distribution of enzyme activity suggests that a genetic polymorphism for monoamine oxidase may control levels of activity expressed in fibroblasts.

The effect of sonication upon monoamine oxidase-A and -B in the rat liver

The effect of sonication upon the activity and properties of monoamine oxidase (MAO) was investigated. Short bursts of sonication produced a preparation of MAO that did not sediment upon centrifugation at 100,000 g for 60 min. The properties of the MAO in the high-speed supernatant fractions were essentially the same as those found for the enzyme in crude homogenates. However, the use of photon correlation spectroscopy to estimate particle size indicated that the MAO in the high-speed supernatant fractions was not soluble, but was localized in a particle of size in the range of 250–660 Å.

Properties of monoamine oxidase (MAO) in human blood platelets, plasma, lymphocytes and granulocytes

The properties of monoamine oxidase in plasma, platelets, lymphocytes and granulocytes have been studied using cells prepared from a single small (about 20 ml) sample of blood. The three substrates, 5-hydroxytryptamine, tyramine and benzylamine, have been used to obtain a more complete picture of blood monoamine oxidase than was previously possible. Measurement of Michaelis constants, use of selective inhibitors, and activity against the three substrates, distinguished three types of activity. The monoamine oxidases in platelets and lymphocytes are very similar, being most active with tyramine or benzylamine as substrate and inhibited by low concentrations of deprenil. The enzymes in plasma and granulocytes are similar in their relatively high activity against 5-hydroxytryptamine and in their inhibition by semicarbazide and cuprizone with tyramine or benzylamine as substrates. They differ in their affinities for 5-hydroxytryptamine and their activity against tyramine. The activity in platelets, plasma, lymphocytes and granulocytes has been measured in a group of 15 normal subjects using three substrates.

Properties of monoamine oxidase in mouse neuroblastoma N1E-115 cells

Monoamine oxidase (MAO) from adrenergic mouse neuroblastoma N1E-115 cells was compared to MAO found in rat and mouse brain, rat superior cervical ganglion, and human platelet. In comparison to MAO from brain and ganglion, mouse neuroblastoma MAO deaminated 5-hydroxytryptamine (5-HT) to a proportionately greater extent than all other substrates studied, with benzylamine deamination representing only 1 per cent that of 5-HT. Neuroblastoma MAO was over 1000 times more sensitive to inhibition by clorgyline than by deprenyl. With increasing concentrations of clorgyline, inhibition of tyramine deamination was represented by a simple sigmoid curve, suggesting the presence of primarily one form of MAO. Our results are consistent with evidence for a specific form of MAO associated with sympathetic neurons and suggest that neutoblastoma N1E-115 cells are highly enriched in MAO type A.

Properties of monoamine oxidase in nerve endings from two bovine brain areas

Monoamine oxidase activity was localized in various subcellular fractions of bovine thalamus and hypothalamus. The recovery of MAO activity was found to parallel two mitochondrial enzymes and was separable from two marker enzymes for the plasma membrane. The MAO activity was found to be higher in the synaptosomes prepared from the hypothalamus compared to the thalamus. These differences in activities were not found for the two other mitochondrial enzymes. Michaelis constants were determined for serotonin and norepinephrine by several methods, both in whole and sonically disrupted mitochondria. Experiments monitoring the deamination of one substrate for MAO, in the presence of a second substrate, and heat denaturation studies demonstrated the presence of two interacting sites for the metabolism of serotonin and norepinephrine in intact mitochondria. The characteristics of these sites were found to depend on the integrity of the mitochondrial membrane.

Cardiac Monoamine Oxidase in Rat

THE monoamine oxidase (MAO) of the rat heart exhibits the unusual property of increasing in activity with increasing age and weight1. This property is not shared by the liver or brain; these organs reach a maximum MAO activity early in life and presumably maintain these levels for the rest of the animal's life span. This communication presents further information about the properties of MAO in the rat heart and its comparison with other tissues and species of animals.

Purification and properties of monoamineoxidase.

Mitochondrial monoamineoxidase from beef liver has been purified twenty-fold. The enzyme was shown to be metal-dependent by using phenanthroline as an inhibitor. The Lineweaver-Burk treatment suggests a non-competitive inhibition. The same procedure applied to phenylcyclopropylamine shows a strictly competitive and irreversible inhibition, and the pH-activity curve suggests further the presence of two monoamineoxidases. The differential action of oxygen and potassium cyanide on iproniazid and phenylcyclopropylamine inhibition of the enzyme has been studied, and the phenylcyclopropylamine inhibition was shown to be independent of oxygen and potassium cyanide. The significance of these experiments is discussed.

Purification and properties of monoamineoxidase

Abstract Mitochondrial monoamineoxidase from beef liver has been purified twenty-fold. The enzyme was shown to be metal-dependent by using phenanthroline as an inhibitor. The Lineweaver-Burk treatment suggests a non-competitive inhibition. The same procedure applied to phenylcyclopropylamine shows a strictly competitive and irreversible inhibition, and the pH-activity curve suggests further the presence of two monoamineoxidases. The differential action of oxygen and potassium cyanide on iproniazid and phenylcyclopropylamine inhibition of the enzyme has been studied, and the phenylcyclopropylamine inhibition was shown to be independent of oxygen and potassium cyanide. The significance of these experiments is discussed.