Exocyclic-keto reductase activities for progesterone and S-warfarin in hepatic microsomes from adult male rats

Hepatic microsomal enzyme activity in the koala and tammar wallaby: high 17beta-hydroxysteroid oxidoreductase activity in koala liver microsomes

We have studied the hepatic microsomal xenobiotic metabolising capacity of koala (Phascolarctos cinereus) and tammar wallaby (Macropus eugenii). Total cytochrome P450 content in hepatic microsomes from koala (0.87 +/- 0.18 nmol/mg protein, n = 4, mean (S.D.) and rat were comparable while tammar wallaby displayed reduced P450 content (0.24 +/- 0.04 nmol/mg protein). Associated microsomal activities (NADPH cytochrome P450 reductase, aminopyrine N-demethylation, aniline hydroxylation, and androstenedione 6beta- and 16alpha-hydroxylation) in koala liver were similar to or reduced relative to rat. Hepatic microsomal NADPH-supported 17beta-hydroxysteroid oxidoreductase (17beta-HSOR) activity was significantly higher in koala (9.99+/-3.08 nmol/mg protein/min) than in tammar wallaby liver (0.86 +/- 0.16 nmol/mg protein/min). However, when NADH was utilised as cofactor the activity was similar in both marsupial species (koala, 1.44 +/- 0.84 nmol/mg protein/min; tammar wallaby, 1.52 +/- 0.44 nmol/mg protein/min). Michaelis-Menten parameters for the kinetics of 17beta-HSOR androstenedione reduction by NADPH and NADH were determined in the koala. The Km for androstenedione was of the order of 1.9-4 microM (n = 4) irrespective of the cofactor used, whilst the Km for NADPH was 0.04-0.05 microM (n = 2) and for NADH was 134-430 microM (n = 2). Potential inhibitors were evaluated for their effects on NADPH-mediated 17beta-HSOR activity with menadione and, to lesser extents, menthone, benzaldehyde and metyrapone eliciting significant inhibition. From detailed kinetic studies menthone was found to be an uncompetitive inhibitor of the activity in koala liver (Ki 220 microM).

Adult-male-specific S-warfarin (11S-OH) and progesterone (20 beta-OH) keto-reductases in rat hepatic microsomes are not identical

Adult-male-specific reductase activities in rat hepatic microsomes use NADPH to reduce S-warfarin and progesterone to their 11S-OH and 20 beta-OH products, respectively (Apanovitch et al. (1992) Biochem. Biophys. Res. Commun. 184, 338-346). When microsomes were treated with increasing concentrations of detergent, S-warfarin (11S-OH) reductase (SW(11S)R) activity was subject to monophasic activation by Triton X-100, monophasic inhibition by sodium cholate, and, activation followed by inhibition with either CHAPS or dodecyl-beta-D-maltoside. A non-dialyzable, heat-sensitive factor in rat and rabbit sera activates microsomal SW(11S)R activity six- to eight-fold. Similar detergent inhibitions but no detergent or serum activations were observed for progesterone (20 beta-OH) reductase (P(20 beta)R) activity. A significant amount of SW(11S)R activity was lost during purification regardless of whether the detergent used for solubilization was activating or inhibiting. Octyl-Sepharose, hydroxyapatite, DEAE-cellulose and carboxymethyl matrices were used to partially purify SW(11S)R. P(20 beta)R activity co-purified with SW(11S)R and the most purified fraction contained two major and several minor polypeptides. Partially purified SW(11S)R is activated by detergents, serum, and salt. These and previous results indicate that SW(11S)R and P(20 beta)R are not identical even though they are both adult male-specific, integral membrane proteins apparently having their active sites exposed on the cytoplasmic surface of the endoplasmic reticulum.