Evidence for O-dealkylation of 7-pentoxyresorufin by cytochrome P450 2B1/2B2 isoenzymes in brain

O-dealkylation of 7-pentoxyresorufin (PR) was studied in rat brain to chara cterise the functional activity specific for cytochrome P450 2B1/2B2 isoenz ymes in brain microsomes. Brain microsomes catalyzed the O-dealkylation of PR in the presence of NADPH. Pretreatment with phenobarbital (PB; 80 mg/kg body wt, i.p.x 5 days) resulted in 3-4 fold induction of pentoxyresorufin-O -dealkylase (PROD) activity while 3-methylcholanthrene (MC; 30 mg/kg body w t, i.p. x 5 days) did not produce any significant increase in enzyme activi ty. Kinetic studies revealed that the rate of velocity (V-max) for the O-de alkylation of PR was significantly increased to 2.9 times higher in brain m icrosomes isolated from PB pretreated rats. In vitro studies using metyrapo ne, an inhibitor of P450 2B1/2B2 catalyzed reactions and antibody for hepat ic PB inducible P450s (P450 2B1/2B2) significantly inhibited the activity o f PROD in cerebral microsomes prepared from PB pretreated animals. These st udies suggest that PB inducible isoenzymes of P450, i.e. P450 2B1/2B2 speci fically catalyze the O-dealkylation of PR in brain microsomes.