Premium
Inhibition of Monoamine Oxidase by N ‐Methylisoquinolinium Ion
Author(s) -
Naoi Makoto,
Hirata Yoko,
Nagatsu Toshiharu
Publication year - 1987
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.1471-4159.1987.tb05574.x
Subject(s) - monoamine oxidase , incubation , catabolism , mitochondrion , biochemistry , chemistry , monoamine neurotransmitter , substrate (aquarium) , biosynthesis , enzyme , biology , endocrinology , medicine , serotonin , ecology , receptor
N ‐Methylisoquinolinium ion (N‐MIQ) has been found to inhibit the biosynthesis of catecholamines; it inhibited tyrosine hydroxylase activity in striatal tissue slices. In this article, the effects of N‐MIQ and an analogue, N ‐methylquinolinium ion, on monoamine oxidase (MAO) activity were examined to see their effects on the catabolism of catecholamines. MAO‐A in human placental mitochondria was strongly inhibited by N‐MIQ in competition with the substrate. The apparent K i value of N‐MIQ was found to be 20.4 ±1.1 μ M , whereas that of N ‐methylquinolinium ion was 54.6 ± 4.5 μ M. MAO‐B in human brain synaptosomes and liver mitochondria was found to be inhibited by N‐MIQ, but the inhibition proved to be noncompetitive. The inhibition of MAO‐B by N‐MIQ was completely reversible by dialysis of the incubation mixture. MAO‐A in human brain and liver mitochondria was more sensitive to the inhibitor than MAO‐B. By quantitative analysis of N‐MIQ, using HPLC, it was found not to be catabolized by the incubation with mitochondria, suggesting that the inhibition was due to N‐MIQ itself and not due to any metabolic product. The inhibition of MAO by N‐MIQ is discussed in terms of its possible involvement of the etiology of parkinsonism.