Deamination of Aliphatic Amines by Monoamine Oxidase A and B Studied Using a Bioluminescence Technique

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Abstract
Deamination of n‐octylamine and n‐decylamine has been studied in various tissues using a new bioluminescence technique. Selectivity of n‐octylamine and n‐decylamine as substrates for monoamine oxidase (MAO) A or B has been determined using both clorgyline and (–)‐deprenyl inhibition curves and kinetic parameters. Homogenates of rat brain, liver and heart containing predominantly MAO‐A or ‐B were prepared by preincubation for 60 min with (–)‐deprenyl or clorgyline (30 nM), respectively. Human placenta (MAO‐A) and platelet (MAO‐B) were used as reference tissues containing only one MAO form. In tissues (rat liver, brain) containing both MAO forms in equal proportion, inhibition curve studies showed a preference of both substrates for the B form of the enzyme; however, where MAO‐A was the major form (rat heart, human placenta), clorgyline was the more effective inhibitor. In the beef brain cortex n‐octylamine showed marked preference for MAO‐B, whereas n‐decylamine was selective toward MAO‐A. Kinetic studies in general supported the picture of greater selectivity of the aliphatic amine substrates for deamination by MAO‐B, as reflected by lower Km values for this enzyme type. However, n‐octylamine was more selective for MAO‐B than n‐decylamine in both kinetic and inhibition curve studies. The deamination of these aliphatic amine substrates cannot be explained only by reference to the binary classification of MAO into types A and B.