Different sensitivity of mitochondrial and cytosolic monoamine oxidases to in vivo but not in vitro inhibition by specific irreversible inhibitors.

The sensitivity of mitochondrial and cytosolic monoamine oxidase (MAO) activities to inhibition by specific irreversible inhibitors was investigated. There were no significant differences in the sensitivity of MAO A and MAO B activities of these fractions to selective inhibitors. However, in vivo administration of pargyline caused a much more potent inhibition of cytosolic MAO than the mitochondrial enzymes. This suggests that cytosolic MAO activity does not represent an artifact (e.g. a product of proteolytic degradation) appearing after tissue homogenisation. The higher sensitivity of cytosolic MAO to inhibitors also points to different routes for pargyline to inhibit MAO in these subcellular fractions.