Studies on the metabolic N- and O-demethylation of [6-3H]codeine

P. H. Duquette, F. J. Peterson, D. L. Crankshaw, N. J. Lindemann, J. L. Holtzman

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We have modified our radiometric assay for ethylmorphine N-demethylase to examine the metabolism of codeine. We find that the current assay gives excellent separation of metabolites with a zero time activity of 0.08%. The N- and O-demethylations are linear for up to 30 min with up to 1 mg/ml of microsomal protein. The pH profiles show slightly different maxima (N-demethylation, pH 8.0; O-demethylation, pH 7.8). The kinetic parameters for N-demethylation were markedly higher (V(max) = 5.6 nmol/min/mg protein; K(M) = 714 μM) than those for O-demethylase (V(max) = 0.75 nmol/min/mg protein; K(M) = 149 μM). These data suggest that the HCHO results primarily from the N-demethylase. Further, the differences in the kinetic parameters and the pH profile suggest that these two activities are catalyzed by different enzymatic systems.

Original languageEnglish (US)
Pages (from-to)477-480
Number of pages4
JournalDrug Metabolism and Disposition
Issue number5
StatePublished - Dec 27 1983


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