Beta-phenylethylamine and benzylamine as substrates for human monoamine oxidase A: A source of some anomalies?
Monoamine oxidase (MAO) A predominates both in human placenta and lung. With 5-hydroxytryptamine (5-HT), beta-phenylethylamine (PEA) and benzylamine (Bz) as substrates and clorgyline and deprenyl, respectively, as selective MAO A and B inhibitors, their activity pattern has been defined and compared with that of human liver. PEA had a much higher V(max) with placental MAO A than did Bz; it behaved largely as an A substrate in placenta, and partly as an A substrate in lung. At commonly used substrate concentrations, deamination of Bz (sensitive to 10(-7) M deprenyl) was a better indicator of MAO B activity than deamination of PEA. The divergence between PEA and Bz as MAO A and B substrates may be one reason for some of the apparent discrepancies in the behaviour of MAO A and B noted in a variety of tissues in the literature. However, Bz reacts with benzylamine oxidase (BzAO) as well as MAO B. Depending on the tissue, deprenyl-resistant Bz activity may indicate the presence of BzAO rather than MAO A. As there is a widespread distribution of BzAO in man and rat, BzAO should be considered among the alternatives of enzyme activity when Bz is used as substrate.
Lewinsohn
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R
Bernhard Baron Memorial Research Laboratories and Institute of Obstetrics and Gynaecology, Queen Charlotte's Maternity Hospital, London W6 0XG, UK.
Glover
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Sandler
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M
D001596:Benzylamines / Q000494:pharmacology*; D003010:Clorgyline / Q000494:pharmacology; D003641:Deamination; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D006801:Humans; D007700:Kinetics; D008995:Monoamine Oxidase / Q000378:metabolism*; D010627:Phenethylamines / Q000494:pharmacology*; D010920:Placenta / Q000201:enzymology; D011247:Pregnancy; D012642:Selegiline / Q000494:pharmacology; D013379:Substrate Specificity; D014018:Tissue Distribution
D001596:Benzylamines; D004791:Enzyme Inhibitors; D010627:Phenethylamines; D012642:Selegiline; C029261:phenethylamine; C030796:benzylamine; D008995:Monoamine Oxidase; D003010:Clorgyline