Dopamine and Norepinephrine MetabolismEither monoamine oxidase A (MAO) or catechol-O-methyltransferase (COMT) can catalyze the first step in catecholamine catabolism. The potentially toxic aldehyde intermediate generated in the MAO reaction (3,4-dihydroxyphenylacetaldehyde for dopamine, 3,4-dihydroxyphenylglycolaldehyde for norepinephrine) is either rapidly reduced to an alcohol (by