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[ 3 H]HARMALINE AS A SPECIFIC LIGAND OF MAO A—I. PROPERTIES OF THE ACTIVE SITE OF MAO A FROM RAT AND BOVINE BRAINS
Author(s) -
Nelson D. L.,
Herbet A.,
Pétillot Y.,
Pichat L.,
Glowinski J.,
Hamon M.
Publication year - 1979
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.1471-4159.1979.tb02296.x
Subject(s) - harmaline , monoamine oxidase , pargyline , tryptamine , clorgyline , chemistry , harmine , binding site , monoamine oxidase b , serotonin , stereochemistry , phenelzine , biochemistry , pharmacology , enzyme , biology , receptor
Abstract A high‐affinity (K d = 5.9 nM) specific binding site for [ 3 H]harmaline was detected in membranes from rat and bovine brains. Studies of the regional and subcellular distributions of this binding indicated its close association with monoamine oxidase type A activity (MAO A) measured with [ 3 H]serotonin ([ 3 H]5‐HT) as the substrate. Maximal binding capacity and MAO A activity were found in mitochondrial enriched fractions. Mitochondria of synaptosomal or extra‐synaptosomal origin exhibited very similar properties with respect to [ 3 H]harmaline binding characteristics and MAO A activity. Among psychoactive drugs, only monoamine oxidase inhibitors (MAO I) prevented the specific binding of [ 3 H]harmaline. Logit‐log inhibition curves of binding by MAO I gave only one slope which was not significantly different from 1.0, suggesting the existence of only 1 category of specific sites for [ 3 H]harmaline in the membrane preparations from rat and bovine brains. Consistent with the preferential inhibition of MAO A by harmaline, other MAO I of this class, i.e. clorgyline and Lilly 51641, were 10 2 ‐2 × 10 3 times more efficient than deprenyl and pargyline, two inhibitors of MAO type B, in displacing [ 3 H]harmaline from its specific binding site. K i and IC 50 values for the inhibition of [ 3 H]harmaline binding by MAO I and MAO substrates (tryptamine, 5‐HT, norepinephrine) were almost identical with those characterizing their action on MAO A activity with [ 3 H]5‐HT as the substrate. In conclusion, the specific binding site for [ 3 H]harmaline exhibited all the expected properties of the active site of MAO A. Like the technique of precipitation with a specific antibody, binding of [ 3 H]harmaline should be of great help for studying the structural characteristics of the active site of MAO A and determining the number of MAO molecules in tissues under various physiological conditions.