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.
Bernhard Baron Memorial Research Laboratories and Institute of Obstetrics and Gynaecology, Queen Charlotte's Maternity Hospital, London W6 0XG, UK.
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Lewinsohn
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Glover
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Sandler
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