title: Characterization of brain beta-carboline-2-N-methyltransferase, an enzyme that may play a role in idiopathic Parkinson's disease.
abstract: The activity of beta-carboline-2-N-methyltransferase results in the formation of neurotoxic N-methylated beta-carbolinium compounds. We have hypothesized that these N-methylated beta-carbolinium cations may contribute to the development of idiopathic Parkinson's disease. This report describes experiments undertaken to optimize assay conditions for bovine brain beta-carboline-2-N-methyltransferase activity. The activity of beta-carboline-2-N-methyltransferase is primarily localized in the cytosol, has a pH optimum of 8.5-9, and obeys Michaelis-Menten kinetics with respect to its substrates, 9-methylnorharman (9-MeNH) and S-adenosyl-L-methionine (SAM). Kinetic constants, KM and Vmax, with respect to 9-MeNH, are 75 microM and 48 pmol/h/mg protein, respectively. The KM for SAM is 81 microM and the Vmax is 53 pmol/h/mg protein. In addition, enzyme activity is inhibited by S-adenosyl-L-homocysteine (SAH) or zinc, and is increased 2-fold in the presence of iron or manganese. Enzyme characterization is a prerequisite to the purification of this N-methyltransferase from bovine brain as well as comparison of its activity in human brain from control and Parkinson's disease individuals.
authors.affiliation: Department of Molecular and Cellular Biochemistry, Loyola University Chicago Medical Center, Maywood, Illinois 60153, USA.
authors.forename: D A
authors.initials: DA
authors.lastname: Gearhart
authors.forename: E J
authors.initials: EJ
authors.lastname: Neafsey
authors.forename: M A
authors.initials: MA
authors.lastname: Collins
mesh_terms: D000818:Animals; D001921:Brain / Q000201:enzymology* / Q000648:ultrastructure; D002243:Carbolines; D002417:Cattle; D003600:Cytosol / Q000201:enzymology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006247:Harmine / Q000031:analogs & derivatives / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008745:Methylation; D008780:Methyltransferases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010300:Parkinson Disease / Q000201:enzymology*; D012435:S-Adenosylhomocysteine / Q000494:pharmacology; D012436:S-Adenosylmethionine / Q000378:metabolism; D015032:Zinc / Q000494:pharmacology
chemical_list: D002243:Carbolines; D004791:Enzyme Inhibitors; D006247:Harmine; D012436:S-Adenosylmethionine; C010262:norharman; D012435:S-Adenosylhomocysteine; D008780:Methyltransferases; C105799:beta-carboline-2-N-methyltransferase; D015032:Zinc