COMT and Parkinson disease: Of mitochondrial substrates specific to mouse neurons, we interestingly detected ubiquitylation of enzymes linked to dopamine and catecholamine metabolism including monoamine oxidase A (MAO-A), MAO-B, and catechol-O-methyltransferase (COMT), which degrade dopamine and are established drug targets for symptomatic treatment of PD (table S2).