Monoamine oxidase in adult Ascaridia galli

Monoamine oxidase (MAO), catalysing oxidative deamination of biogenic monoamines, has been detected in adult Ascaridia galli. MAO was present in mitochondria and deaminated noradrenaline at the maximal rate, although serotonin, adrenaline, tyramine and dopamine were also degraded but more slowly. Of the organs studied, the body wall, female reproductive organ and intestine, the body wall (containing neuronal structures) showed highest MAO activity. Km value for chick ascarid mitochondrial MAO using tyramine as substrate was 1.66 X 10(-3) M and it was most active at 2.5 mM tyramine concentration, pH 7.5 and 40 degrees C. MAO of A. galli appeared to be thermolabile as nearly 80% of its activity was lost when the incubation temperature was increased 5 degrees above optimum.     

Monoamine oxidase and mitochondrial respiration

Mitochondrial defects encompassing complexes I-IV of the electron transport chain characterize a relatively large number of neurodegenerative diseases. The relationships between mitochondrial lesions and recently described genetic alterations have not yet been defined. We describe a general mechanism whereby the enzymatic metabolism of neurotransmitters by monoamine oxidase (MAO) damages mitochondria, altering their protein thiol status and suppressing respiration. In these experiments, incubation of rat brain mitochondria with tyramine (a mixed MAO-A/MAO-B substrate) for 15 min at 27 degrees C suppressed state 3 respiration by 32.8% and state 5 respiration by 40.1%. These changes were accompanied by a 10-fold rise in protein-glutathione mixed disulfides. Direct comparison of effects on respiration and MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] dye reduction during electron flow gave similar results. It is suggested that certain mitochondrial lesions may derive from the natural turnover of monoamine neurotransmitters in susceptible individuals.     

Monoamine oxidase inhibitory properties of milacemide in rats

Milacemide is a glycine prodrug with reported antiepileptic antimyoclonic properties. In this study, milacemide increased "wet dog shakes" in rats pretreated with 5-Hydroxytryptophan (5-HTP) and carbidopa. Moreover, it worsened the serotonin behavior syndrome precipitated by 5-HTP and the monoamine oxidase inhibitor tranylcypromine. The serotonin syndrome was also elicited by the combination of milacemide and 5-HTP without tranylcypromine. In vitro, milacemide inhibited both monoamine oxidase A and B from the frontal cortex of rats, to a greater extent for MAO B. This drug is currently under investigation in humans as an antiepileptic agent and precautions for the consequences of monoamine oxidase inhibition should be considered when the drug is used in high doses.     

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.     

Monoamine oxidase inhibitors from Gentiana lutea

Three monoamine oxidase (MAO) inhibitors were isolated from Gentiana lutea. Their structures were elucidated to be 3-3'linked-(2'-hydroxy-4-O-isoprenylchalcone)-(2'-hydroxy-4'-O-isoprenyldihydrochalcone) (1), 2-methoxy-3-(1,1'-dimethylallyl)-6a,10a-dihydrobenzo(1,2-c)chroman-6-one and 5-hydroxyflavanone. These compounds, and the hydrolysis product of 1, displayed competitive inhibitory properties against MAO-B which was more effective than MAO-A.