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Specificity of Endogenous Substrates for Types A and B Monoamine Oxidase in Rat Striatum
Author(s) -
Schoepp Darryle D.,
Azzaro Albert J.
Publication year - 1981
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.1471-4159.1981.tb10829.x
Subject(s) - clorgyline , monoamine oxidase , in vivo , monoamine oxidase b , deamination , biochemistry , oxidative deamination , serotonin , chemistry , enzyme , striatum , tyramine , substrate (aquarium) , dopamine , biology , endocrinology , receptor , ecology , microbiology and biotechnology
Studies were designed to evaluate specificity of the transmitter amines serotonin (5‐hydroxytryptamine, 5‐HT) and dopamine (DA), as well as the trace amines p ‐tyramine ( p ‐TA) and β ‐phenylethylamine (PEA) for types A and B monoamine oxidase (MAO) in rat striatum. 5‐HT was found to be a specific substrate for the type A enzyme. However, the specificity of PEA for the type B enzyme was found to be concentration‐dependent. When low concentrations of PEA and 5‐HT were used to measure type B and type A activities, respectively, both clorgyline and deprenyl were highly selective for the sensitive form of MAO in vivo. However, as the concentration of PEA was increased, the type B inhibitor deprenyl became less effective in preventing deamination of PEA. Conversely, the type A inhibitor clorgyline became more effective in this regard. Kinetic analysis following selective in vivo inhibition showed PEA deamination by both forms of MAO with a 13‐fold greater affinity for the type B enzyme. In vivo dose‐response curves obtained with the common substrates DA and p ‐TA showed approximately 20% deamination by the B enzyme. Kinetic values for DA and p ‐TA deamination in in vivo ‐treated tissue possessing only type A or type B MAO activity, revealed a 2.5‐fold greater affinity for the type A enzyme. These studies show the importance of concentration on substrate specificity in striatal tissue. The results obtained characterize the common substrate properties of DA and p ‐TA as well as of PEA in rat striatum. In addition, the presence of regional specificity for 5‐HT deamination by only type A MAO is demonstrated.