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Oxidation of N ‐Methyl‐1,2,3,4‐Tetrahydroisoquinoline into the N ‐Methyl‐Isoquinolinium Ion by Monoamine Oxidase
Author(s) -
Naoi Makoto,
Matsuura Sadao,
Parvez Hasan,
Takahashi Tsutomu,
Hirata Yoko,
Minami Masayasu,
Nagatsu Toshiharu
Publication year - 1989
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1989.tb09170.x
Subject(s) - monoamine oxidase , chemistry , enzyme , tetrahydroisoquinoline , monoamine oxidase b , substrate (aquarium) , tyrosine , tyrosine hydroxylase , monoamine oxidase a , metabolism , stereochemistry , biochemistry , medicinal chemistry , biology , ecology
N ‐Methyl‐1,2,3,4‐tetrahydroisoquinoline (NMTIQ) was found to be oxidized by monoamine oxidase (MAO) into N ‐methylisoquinolinium ion, which was proved to inhibit enzymes related to the metabolism of catecholamines, such as tyrosine hydroxylase, aromatic‐L‐amino acid decarboxylase, and MAO. NMTIQ was oxidized by both types A and B MAO in human brain synaptosomal mitochondria. Oxidation was dependent on the amount of MAO sample and the reaction time. Enzyme activity with respect to NMTIQ reached optimum at a pH of ∼7.25, as was the case with other substrates. Type A MAO had higher activity for this substrate than type B. The K m and V max values of the oxidation by types A and B MAO were 571 ± 25 μ M and 0.29 ± 0.06 pmol/min/mg protein, and 463 ± 43 μ M and 0.16 ± 0.03 pmol/min/mg protein, respectively. The V max values of types A and B MAO for NMTIQ were much smaller than those for other substrates such as kynuramine. NMTIQ was the first tetrahydroisoquinoline shown to be oxidized into the isoquinolinium ion by MAO in the brain.