Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: HUMANGGP:001709 (MAO-A)
 2,432 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Monoamine oxidase (MAO) was characterized in tissue homogenates from pancreatic islets, exocrine pancreas, and liver from rats. Phenylethylamine was preferentially deaminated by pancreatic islet MAO while 5-hydroxytryptamine was preferentially deaminated by MAO from exocrine pancreas, and tyramine was a good substrate for both tissues. All three substrates were well deaminated by liver tissue. Clorgyline, a selective inhibitor of MAO-A, preferentially inhibited deamination of 5-hydroxytryptamine by all three tissue homogenates, while deprenyl, a selective inhibitor of MAO-B, preferentially inhibited deamination of phenylethylamine. In the case of pargyline, a less selective MAO-B inhibitor, the preference in favour of phenylethylamine was less pronounced. According to these results, MAO in pancreatic islets can be classified as predominantly type B enzyme species and MAO in exocrine pancreas as predominantly type A enzyme species while both types of the enzyme are present in the liver. Using the same three MAO substrates and compared with the effects of the selective enzyme inhibitors, clorgyline and deprenyl, tranylcypromine can be classified as a potent nonselective inhibitor of MAO in homogenates of all three tissues investigated with a slight preference in favour of the inhibition of the B-form of the enzyme, while in contrast amezinium can be classified as a weak nonselective inhibitor of MAO with a slight preference in favour of the inhibition of the A-form of the enzyme. All MAO inhibitors tested also inhibited insulin secretion by isolated incubated rat pancreatic islets, however only at IC50 which were two to three decimal powers higher than those necessary for the inhibition of the MAO activity, thus indicating that inhibition of MAO activity and inhibition of insulin secretion are apparently not closely related.
 ...
PMID:Monoamine oxidase in pancreatic islets, exocrine pancreas, and liver from rats. Characterization with clorgyline, deprenyl, pargyline, tranylcypromine, and amezinium. 641 32

A fast and sensitive assay for the determination of monoamine oxidase activity was developed. The method is based on the separation and quantitation of 14C-labeled assay products by high-performance liquid chromatography, which is interfaced directly into a flow-through radioactivity detector. This allows on-line quantitation of the radioactive compounds with picomole sensitivity. The method makes possible the complete separation and detection of the deaminated products of monoamine oxidase A and B substrates benzylamine and 5-hydroxytryptamine, respectively. This assay has been applied to the measurement of monoamine oxidase A and B activities in rat brain.
 ...
PMID:On-line radiochemical assay for monoamine oxidase utilizing high-performance liquid chromatography. 644 38

Cell fractions enriched in cardiac muscle cells (myocytes), on the one hand, and in non-myocytes, on the other, were prepared by dissociation of rat ventricular tissue with collagenase. Amine oxidase activities in homogenates of these cell fractions and also in homogenates of the corresponding undissociated ventricular tissue were compared. In addition, the activity of alkaline phosphatase (AP), an enzyme found predominantly associated in the heart with non-myocytes, particularly capillary endothelial cells, was also measured. No significant difference in the activity of MAO-A (assayed with 1 mM 5-hydroxytryptamine) was found between myocyte and non-myocyte fractions. In contrast, the activities of alkaline phosphatase (AP) and also the semicarbazide-sensitive amine oxidase (SSAO), assayed with 1 microM benzylamine (BZ), were both significantly higher in non-myocytes, by several-fold, than in myocyte fractions. Studies of the inhibition by clorgyline of 1 mM BZ metabolism confirmed that both MAO-A and MAO-B can also contribute to BZ oxidation in the rat heart. These experiments indicated different ratios of MAO-A: MAO-B in the various cell fractions. The ratios of the percentage contributions of MAO-A and MAO-B, respectively, to the total metabolism of 1 mM BZ were 78:20 (myocytes), 43:52 (non-myocytes) and 57:32 (undissociated tissue). These results suggest that MAO-B, in addition to AP and SSAO, may be associated preferentially with non-myocyte constituents of the rat heart. Although cardiac myocytes appear to contain predominantly MAO-A, this enzyme form is also localized, with high activity, to the non-myocyte fraction. However, since the non-myocyte fraction is heterogeneous in its cell content, containing vascular components of the coronary microcirculation, as well as other cells of connective tissue origin, the exact cellular localization of the enzyme activities within this fraction has not yet been defined.
 ...
PMID:Monoamine oxidase activities of dissociated cell fractions from rat ventricular muscle. 646 72

Developmental changes in monoamine oxidase (MAO) activity in the mouse brain were investigated with the substrates beta-phenylethylamine (PEA), tryptamine, and 5-hydroxytryptamine (5-HT). In the newborn brain, MAO activity towards PEA was found to be much lower than the adult and to be inhibited by clorgyline in a double-sigmoidal fashion. The inhibition curve shifted to a single-sigmoidal pattern with age. MAO activity towards 5-HT as substrate was inhibited by 90% and in a single-sigmoidal manner by clorgyline throughout the postnatal life. Lineweaver-Burk plots with PEA as substrate presented two linear lines (apparent Km: 28.6 and 4.1 microM) for the newborn and one line (apparent Km: 11.4 microM) for the adult, respectively. The plot with high Km value for the newborn brain disappeared in a clorgyline-treated preparation. These findings suggest that age-dependent alterations in the ratio of MAO-A/MAO-B activity affect the substrate specificity of the enzyme.
 ...
PMID:Developmental changes in the activity and substrate specificities of mouse brain monoamine oxidase. 647 64

In in vivo and in vitro experiments the effects of some heavy metal salts (Cu, Co, Cd, Pb, Ni, Zn, Hg, As, Bi and Sn) on rat liver and brain mitochondrial monoamine oxidase (MAO) activity was studied using three different substrates (tyramine, 5-hydroxytryptamine (5-HT) and beta-phenylethylamine (2-PEA). It was established that some of the metals (Cu, Cd, Bi) inhibited MAO activity both in vivo and in vitro experiments, others like Ni, Zn, As and Sn inhibited it only in vivo while Hg exerted inhibitory action only in vitro. The in vivo experiments showed significantly higher sensitivity of brain MAO as compared with liver MAO to the inhibitory action of metals. The same higher susceptibility was shown by liver and brain MAO-A form. It was concluded that the inhibitory effects of some heavy metal salts on MAO activity were not directly connected with their action on enzyme thiol groups but more probably with changes in the enzyme membrane surroundings in the different organs.
 ...
PMID:Changes in rat liver and brain monoamine oxidase activity after acute treatment with some heavy metal salts. 652 14

Brain levels of 5-hydroxytryptamine (5-HT), tryptamine (T), 2-phenylethylamine (PEA) and monoamine oxidase activity at 5, 15, 30, 60, 120 and 240 min were determined in male Sprague-Dawley rats after intraperitoneal injection of the "pro-drug" N-2-cyanoethyltranylcypromine (CE-TCP, dose 0.1 mMole/kg). Analyses of 5-HT, T and PEA were performed on an electron-capture gas chromatograph with a capillary column. Activity of MAO-A and MAO-B was measured using a radiochemical method. Results indicate substantial inhibition of MAO in rat brain after intraperitoneal administration of CE-TCP, leading to elevated levels of 5-HT, T and PEA as early as 5 min after drug administration. Increases in brain levels of the trace amines T and PEA were much greater (approximately 40 and 100 times control levels, respectively) than with 5-HT (approximately 1.8 times control level) 240 min after administration of CE-TCP.
 ...
PMID:Brain levels of 5-hydroxytryptamine, tryptamine and 2-phenylethylamine in the rat after administration of N-cyanoethyltranylcypromine. 653 37

The present study was undertaken to clarify the enzymic and molecular properties of monoamine oxidase (MAO) in carp brain. In particular, its sensitivities to selective MAO inhibitors, kinetic properties and molecular weight were compared with those of the enzyme in carp liver. The selective and potent MAO-A and MAO-B inhibitors FLA 788(+), FLA 336(+), MD 780236 and benzylcyanide caused dose-dependent inhibitions of MAO activity in both carp brain and liver; the inhibition curves were all single-sigmoidal, and the degrees of inhibition of the activities towards 5-hydroxytryptamine (5-HT, selective MAO-A substrate), tyramine (substrate for both forms of MAO) and beta-phenylethylamine (PEA, selective MAO-B substrate) were similar. This was also the case for inhibition of activity in carp brain by the irreversible and selective MAO-A and MAO-B inhibitors clorgyline and I-deprenyl, indicating the presence in both preparations of a single MAO which differs from either form of MAO. Studies on the substrate specificities and Km values for these three substrates and the inhibitory effects of some compounds suggested that the enzymic characters of MAO in carp preparations were similar and that these enzymes might be FAD-containing enzymes, like MAO in various mammals. By labelling the preparations with radioactive pargyline and then subjecting them to sodium dodecyl sulfate electrophoresis, the apparent molecular weights of carp brain and liver MAO were estimated as 60,000 daltons. The same value was also obtained for rat brain and liver mitochondrial MAO-B. These results indicate that by the present definitions of MAO-A and MAO-B, MAO in carp brain and liver is similar to, but distinct from, both these forms of MAO.
 ...
PMID:Enzymic and molecular characteristics of a new form of monoamine oxidase, distinct from form-A and form-B. 674 74

The characteristics of mitochondrial monoamine oxidase (MAO) in carp liver were studied with MAO inhibitors and substrates. This enzyme was thermolabile, but was stabilized in the presence of bovine serum albumin. With clorgyline and deprenyl, single-sigmoidal curves for inhibition of the activity towards tyramine or 5-hydroxytryptamine were obtained; the sensitivities to the two inhibitors were identical. The activity towards beta-phenylethylamine was not completely inhibited by clorgyline or deprenyl, but the remaining activity was inhibited by semicarbazide and the inhibition curves by either clorgyline or deprenyl and semicarbazide were also identical to the curves with the other two substrates. These results suggest that carp liver mitochondria contain "classical" MAO and a clorgyline- and deprenyl-resistant amine oxidase and that the classical MAO does not seem to be MAO-A or MAO-B, which are present in mitochondria of most mammalian tissues.
 ...
PMID:A new type of mitochondrial monoamine oxidase distinct from type-A and type-B. 682 8

The activities of monoamine oxidases A and B towards 5-hydroxytryptamine and beta-phenethylamine, respectively, were compared in the left and right caudatus, hippocampus, parietal cortex, cerebellum and frontal cortex 6 months after gamma-irradiation (single dose of 23 Gy) of either the right hemisphere or of the whole rabbit brain (in which case, a dose of l6 Gy). No difference in monoamine oxidase A or B activities were found in any of the brain regions.
 ...
PMID:The activity of monoamine oxidases A and B in gamma-irradiated rabbit brains. 705 61

Km and Vmax values of monoamine oxidase (MAO) A and B towards 5-hydroxytryptamine were determined for rat brain homogenates after the in vitro inhibition of one of the two forms by the selective inhibitors clorgyline and l-deprenyl. Km values of 178 and 1170 microM, and Vmax values of 0.73 and 0.09 nmol . mg protein-1 . min-1 towards 5-hydroxytryptamine were found for MAO-A and -B, respectively. The Ki for 5-hydroxytryptamine as a competitive inhibitor of beta-phenethylamine oxidation by MAO-B was found to be 1400 microM. The significance of these findings is discussed.
 ...
PMID:Deamination of 5-hydroxytryptamine by both forms of monoamine oxidase in the rat brain. 705 91


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>