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Updated: Oct 12, 2026

Monitoring the Reductive and Oxidative Half-Reactions of a Flavin-Dependent Monooxygenase using Stopped-Flow Spectrophotometry
Published on: March 18, 2012
Studies on the partially uncoupled oxidation of tetrahydropterins by phenylalanine hydroxylase
1Laboratory of Neurochemistry, National Institute of Mental Health, Bethesda, MD 20892.
Abstract:
The uncoupled portion of the partially uncoupled oxidation of tetrahydropterins by phenylalanine hydroxylase can be described by the same model as we have recently derived for the fully uncoupled reaction (Davis, M.D. and Kaufman, S. (1989) J. Biol. Chem. 264, 8585-8596). Although essentially no hydrogen peroxide is formed during the fully coupled oxidation of tetrahydrobiopterin or 6-methyltetrahydropterin by phenylalanine hydroxylase when phenylalanine is the amino acid substrate, significant amounts of hydrogen peroxide are formed during the partially uncoupled oxidation of 6-methyltetrahydropterin when para-fluorophenylalanine or para-chlorophenylalanine are used in place of phenylalanine. Similarly, during the partially uncoupled oxidation of the unsubstituted pterin, tetrahydropterin, even in the presence of phenylalanine, hydrogen peroxide formation is detected. The 4a-carbinolamine tetrahydropterin intermediate has been observed during the fully uncoupled tyrosine-dependent oxidations of tetrahydropterin and 6-methyltetrahydropterin by lysolecithin-activated phenylalanine hydroxylase, suggesting that this species is also a common intermediate for uncoupled oxidations by this enzyme.
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