- Determination of the mechanism of demethylenation of (methylenedioxy)phenyl compounds by cytochrome P450 using deuterium isotope effects
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The mechanism of demethylenation of (methylenedioxy)benzene (MDB), (methylenedioxy)amphetamine (MDA), and (methylenedioxy)methamphetamine (MDMA) by purified rabbit liver cytochrome P450IIB4 has been investigated by using deuterium isotope effects. A comparison of the magnitude and direction of the observed kinetic isotope effects indicates that the three compounds are demethylenated by different mechanisms. The different mechanisms of demethylenation have been proposed on the basis of comparisons of the observed biochemical isotope effects with the isotope effects from purely chemical systems.
- Fukuto,Kumagai,Cho
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- Identification of the human cytochromes P450 involved in the oxidative metabolism of 'Ecstasy'-related designer drugs
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The human cytochrome P450 (CYP) isozymes catalyzing the oxidative metabolism of the widely abused amphetamine derivatives MDMA (N-methyl-3,4-methylenedioxyamphetamine, 'Ecstasy'), MDE (N-ethyl-3,4-methylenedioxyamphetamine, 'Eve'), and MDA (3,4-methylenedioxyamphetamine) were identified. Using a simplified non-extractive reversed-phase HPLC assay with fluorescence detection, biphasic Michaelis-Menten kinetics were obtained for formation of all three dihydroxyamphetamines in liver microsomes from a CYP2D6 extensive metabolizer subject. In contrast, no low K(m) component was detectable in microsomes from a poor metabolizer subject. Additional specific probes for CYP2D6 further confirmed this isozyme as the exclusive low K(m) component for demethylenation. P450-selective inhibitors applied to CYP2D6-inhibited microsomes and activity measurements in a series of recombinant P450s suggested CYP1A2 as the major high K(m) component with contributions by CYP2B6 and CYP3A4. Moreover, the relative CYP1A2 content of a panel of 12 human livers was weakly but significantly correlated to the high K(m) demethylenase activity (Spearman rank correlation coefficient [r(s)] = 0.58; P 0.05). Microsomal maximal velocities for N-dealkylation were at least 7-fold lower than for demethylenation and were characterized by apparently monophasic kinetics. The most important isozyme for this reaction appeared to be CYP2B6, the microsomal content of which was found to be strongly correlated to N-deethylation of MDE (r(s) = 0.90; P 0.001). We conclude that, in addition to CP2D6 as the sole high-affinity demethylenase, several other P450 isozymes have the capacity to contribute to microsomal oxidative metabolism of methylenedioxyamphetamines. This may be of particular importance in individuals genetically lacking functional CYP2D6. Copyright (C) 2000 Elsevier Science Inc.
- Kreth, Klaus-Peter,Kovar, Karl-Artur,Schwab, Matthias,Zanger, Ulrich M.
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p. 1563 - 1571
(2007/10/03)
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- Aromatic L-Amino Acid Decarboxylase from Micrococcus percitreus Purification, Crystallization and Properties
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An aromatic L-amino acid decarboxylase was crystallized from the cell free extract of Micrococcus percitreus.The purification procedure included protamine sulfate treatment, ammonium sulfate fractionation, DEAE-Sephadex column chromatography and Sephadex G-200 filtration.Crystals were obtained from a solution of the purified enzyme by addition of ammonium sulfate.The crystalline enzyme preparation was homogeneous as judged by ultracentrifugation and SDS-polyacrylamide gel electrophoresis.The molecular weight was determined to be approximately 101,000.The enzyme was evidently composed of two identical subunits of a molecular weight of 48,000.The enzyme catalyzed the stoichiometric conversion of L-tryptophan to tryptamine and CO2 in the presence of pyridoxal phosphate.The optimum pH was 9.0 for the conversion.The Km value and the maximum velocity of L-tryptophan decarboxylation were 2.4E-3 M and 44 μmol/min/mg of protein, respectively.This enzyme also catalyzed decarboxylation of 5-hydroxy-L-tryptophan, L-phenylalanine, L-tyrosine, 3,4-dihydroxy-L-phenylalanine, L-kynurenine and thier α-methyl amino acid derivatives.
- Nakazawa, Hidetsugu,Kumagai, Hidehiko,Yamada, Hideaki
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p. 2543 - 2552
(2007/10/02)
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- Hair dyeing composition containing an aryldiamine and a substituted catechol
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A composition for use in the dyeing of keratinous fibre such as hair includes an aqueous anaerobic solution of an aryldiamine and a substituted catechol. Optionally, an aromatic coupling agent can also be incorporated in the composition to modify the shade of color produced. Anaerobic storage conditions can, for example, be maintained by packing the composition in an aerosol container with a halocarbon propellant.
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