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Med Hypotheses. 2001 Nov;57(5):628-32.

Catecholamine metabolism in the brain by membrane-bound and soluble catechol-o-methyltransferase (COMT) estimated by enzyme kinetic values.

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  • 1Department of Pharmacology and Toxicology, Institute of Biomedicine, Haarmaninkatu 8, Fin-00014, University of Helsinki, Finland.


A kinetic model was constructed to reevaluate the catecholamine metabolism in hypothetical brain homogenates. Earlier published kinetic values of recombinant membrane-bound (MB-) COMT and soluble (S-) COMT were combined with data suggesting that MB-COMT represents 70% and 30% of total COMT protein in human and rat brain, respectively. In the rat brain model L-DOPA and 3,4-dihydroxybenzoic acid were O-methylated mainly via S-COMT, while dopamine and noradrenaline, at low concentrations, were O-methylated slightly more by MB-COMT. In the human brain model dopamine and noradrenaline were metabolized primarily by MB-COMT. The ratio of meta (3-methoxy) over para (4-methoxy) product formation from 3,4-dihydroxybenzoic acid was higher for MB-COMT than S-COMT. It is suggested that MB-COMT clearly predominates the O-methylation of dopamine and noradrenaline also in vivo. Additionally, meta/para ratios could support the enrichment of either isoform of COMT in a homogenate sample.

Copyright 2001 Harcourt Publishers Ltd.

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