Monoamine oxidase (MAO) from adrenergic mouse neuroblastoma N1E-115 cells was compared to MAO found in rat and mouse brain, rat superior cervical ganglion, and human platelet. In comparison to MAO from brain and ganglion, mouse neuroblastoma MAO deaminated 5-hydroxytryptamine (5-HT) to a proportionately greater extent than all other substrates studied, with benzylamine deamination representing only 1 per cent that of 5-HT. Neuroblastoma MAO was over 1000 times more sensitive to inhibition by clorgyline than by deprenyl. With increasing concentrations of clorgyline, inhibition of tyramine deamination was represented by a simple sigmoid curve, suggesting the presence of primarily one form of MAO. Our results are consistent with evidence for a specific form of MAO associated with sympathetic neurons and suggest that neutoblastoma N1E-115 cells are highly enriched in MAO type A.
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