title: Inhibition of monoamine oxidase by 3,4-dihydroxyphenylserine.
abstract: The effects of diastereomers of 3,4-dihydroxyphenylserine (DOPS) on the enzyme activity of monoamine oxidase (MAO) in human placenta and liver mitochondria were examined. Both L- and D-threo-DOPS were found to inhibit MAO-A in human placental mitochondria in competition with the substrate, and the Ki values for L- and D-threo-DOPS obtained were 68.3 and 125 microM, respectively. The inhibitory effect of L-threo-DOPS on both MAO-A and -B activity was confirmed in human liver mitochondria, and MAO-A was found to be more sensitive to the inhibitor. Other isomers of DOPS, L- and D-erythro-DOPS, were found to inhibit MAO activity, but the inhibition was noncompetitive with the substrate. The inhibitory effects of DOPS isomers were not affected by the presence of NSD-1055, an inhibitor of aromatic L-amino acid decarboxylase, suggesting that the inhibition is the direct effect of DOPS, and not of norepinephrine produced by the decarboxylase.
mesh_terms: D003010:Clorgyline / Q000494:pharmacology; D015103:Droxidopa / Q000494:pharmacology*; D005260:Female; D006801:Humans; D007700:Kinetics; D008928:Mitochondria / Q000201:enzymology; D008930:Mitochondria, Liver / Q000201:enzymology; D008995:Monoamine Oxidase / Q000378:metabolism*; D008996:Monoamine Oxidase Inhibitors / Q000494:pharmacology; D010920:Placenta / Q000201:enzymology; D011247:Pregnancy; D012642:Selegiline / Q000494:pharmacology; D012694:Serine / Q000031:analogs & derivatives*; D013237:Stereoisomerism
chemical_list: D008996:Monoamine Oxidase Inhibitors; D012642:Selegiline; D012694:Serine; D008995:Monoamine Oxidase; D015103:Droxidopa; D003010:Clorgyline