Organic solvent extraction of liver microsomal lipid: Effect on the kinetic parameters of benzo[a]pyrene hydroxylase and benzphetamine n-demethylase activity

Extraction of lyophilized hepatic microsomes from untreated rats, once with l-butanol and twice with acetone, increased benzoa]pyrene hvdroxylase and benzphetamine N-demethylase activities by 25 per cent: these activities were increased further by the addition of dilauroylglyceryl-3-phosphorycholine (di-12-GPC). More extensive extraction with 1-butanol decreased the activities by 50 per cent; addition of di-12-GPC restored activity to control levels. Kinetic analysis indicated that a single extraction with 1-butanol decreased the apparent K_m for benzoa]pyrene 6-fold, with no change in V_max; addition of di-12-GPC had no effect on the apparent K_m or V_max. In contrast, a single extraction with l-butanol of microsomes from 3-methycholanthrene (3-MC)-treated rats had no effect on the apparent K_m or V_max for benzoa]pyrene. Lineweaver-Burk plots of benzphetamine 4N-demethylase activity in extracted microsomes from untreated rats and in both unextracted and extracted microsomes from 3-MC-treated rats were non-linear with a marked increase in activity at higher benzphetamine concentrations.