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Cytochrome p‐455 nm complex formation in the metabolism of phenylalkylamines. XII. Enantioselectivity and temperature dependence in microsomes and reconstituted cytochrome p‐450 systems from rat liver
Author(s) -
Jönsson KarlHenrik,
Lindeke Björn
Publication year - 1992
Publication title -
chirality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.43
H-Index - 77
eISSN - 1520-636X
pISSN - 0899-0042
DOI - 10.1002/chir.530040803
Subject(s) - chemistry , microsome , enantiomer , nitroso , cytochrome p450 , cytochrome , stereochemistry , hydroxylamine , hexobarbital , enzyme , medicinal chemistry , organic chemistry
Formation of metabolic intermediate (MI) complexes was studied with the enantiomers of amphetamine, 1‐phenyl‐2‐pentanamine, N ‐hydroxyamphetamine, and 2‐nitroso‐1‐phenylpropane (the C ‐nitroso analogue of amphetamine). Three different enzyme systems were used; liver microsomes from phenobarbital pretreated rats and two reconstituted systems containing the P450 2B1 and P450 2C11 forms of cytochrome P‐450. Enantioselective complex formation in microsomes was shown for the amines and the nitroso compound, but not for the hydroxylamine. The highly purified P450 2B1 system formed the MI complex with all substrates tested, and the enantioselectivity observed with the microsomal system was reproduced. In the P450 2C11 system the nitroso compounds were completely inactive, whereas the enantiomers of N ‐hydroxyamphetamine still produced the complex at a high rate. Changes in temperature were shown to affect (R)‐2‐nitroso‐1‐phenylpropane more than its enantiomer. Both enantiomers showed biphasic Arrhenius plots for MI complex formation in microsomes (breaks around 22°C), but the activation energies of the (R)‐isomer were about five times higher than those of the (S)‐isomer. A theory is presented which suggests different modes of interaction with the active site of P‐450 to account for the different behaviour of the various substrates. © 1992 Wiley‐Liss, Inc.