TY - JOUR
T1 - Hepatic microsomal enzyme activity in the koala and tammar wallaby
T2 - High 17β-hydroxysteroid oxidoreductase activity in koala liver microsomes
AU - Stupans, I.
AU - Kong, S.
AU - Kirlich, A.
AU - Murray, M.
AU - Bailey, E. L.
AU - Jones, B. R.
AU - McKinnon, R. A.
PY - 1999/5/1
Y1 - 1999/5/1
N2 - 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 6β- and 16α-hydroxylation) in koala liver were similar to or reduced relative to rat. Hepatic microsomal NADPH-supported 17β-hydroxysteroid oxidoreductase (17β-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 17β-HSOR androstenedione reduction by NADPH and NADH were determined in the koala. The K(m) for androstenedione was of the order of 1.9-4 μM (n=4) irrespective of the cofactor used, whilst the K(m) for NADPH was 0.04-0.05 μM (n=2) and for NADH was 134-430 μM (n=2). Potential inhibitors were evaluated for their effects on NADPH-mediated 17β-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 (K(i) 220 μM). Copyright (C) 1999 Elsevier Science Inc.
AB - 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 6β- and 16α-hydroxylation) in koala liver were similar to or reduced relative to rat. Hepatic microsomal NADPH-supported 17β-hydroxysteroid oxidoreductase (17β-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 17β-HSOR androstenedione reduction by NADPH and NADH were determined in the koala. The K(m) for androstenedione was of the order of 1.9-4 μM (n=4) irrespective of the cofactor used, whilst the K(m) for NADPH was 0.04-0.05 μM (n=2) and for NADH was 134-430 μM (n=2). Potential inhibitors were evaluated for their effects on NADPH-mediated 17β-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 (K(i) 220 μM). Copyright (C) 1999 Elsevier Science Inc.
KW - 17β-Hydroxysteroid dehydrogenase
KW - 17β-Hydroxysteroid oxidoreductase
KW - Androstenedione
KW - Cytochrome P450
KW - Koala
KW - Tammar wallaby
UR - http://www.scopus.com/inward/record.url?scp=0033004438&partnerID=8YFLogxK
U2 - 10.1016/S0742-8413(99)00012-2
DO - 10.1016/S0742-8413(99)00012-2
M3 - Article
C2 - 10390058
VL - 123
SP - 67
EP - 73
JO - Comparative Biochemistry and Physiology - C Pharmacology Toxicology and Endocrinology
JF - Comparative Biochemistry and Physiology - C Pharmacology Toxicology and Endocrinology
SN - 0742-8413
IS - 1
ER -