TY - JOUR
T1 - Kinetics, activation, and induction of aortic mono-oxygenases-biotransformation of benzo[a]pyrene
AU - Bond, James A.
AU - Omiecinski, Curtis J.
AU - Juchau, Mont R.
PY - 1979
Y1 - 1979
N2 - Aortic aryl hydrocarbon hydroxylase (EC 1.14.14.2), a cytochrome P-450-dependent mono-oxygenase complex potentially important in the etiology of atherosclerosis, was detected previously in aortic homogenates of humans, monkeys and rabbits [M. R. Juchau, J. A. Bond and E. P. Benditt, Proc. natn. Acad. Sci. U.S.A. 73, 3723 (1976)]. The present study more fully characterizes the mono-oxygenase activity in aortas of treated and untreated New Zealand White rabbits. A 2-fold activation was obtained with NADH (7 × 10-4 M) at saturating concentrations of NADPH. Addition of heme (9 μm) increased the enzymatic activity 2- to 4-fold during a 15-min incubation and over 25-fold during a 2-hr incubation. The results suggest the presence of relatively high concentrations of apoprotein in the aortic tissues. Kinetic studies in the presence of heme yielded an apparent Km of 1 × 10-4 M and Vmax of 15.24 pmoles/mg of protein/min with respect to NADPH. A sigmoidal curve was obtained with varying benzo[a]pyrene concentrations (0.5 to 80 μM), suggesting the possibility of allosterism. Aroclor 1254,3-methylcholanthrene and 5,6-benzoflavone acted to induce the cytochrome P-450-dependent mono-oxygenase, while pheno-barbital and pregnenolone 16α-carbonitrile demonstrated little, if any, induction capacity. Analyses of metabolites formed in induced aortas with high-pressure liquid chromatography revealed the formation (in each case) of primarily the phenolic metabolites of benzo[a]pyrene.
AB - Aortic aryl hydrocarbon hydroxylase (EC 1.14.14.2), a cytochrome P-450-dependent mono-oxygenase complex potentially important in the etiology of atherosclerosis, was detected previously in aortic homogenates of humans, monkeys and rabbits [M. R. Juchau, J. A. Bond and E. P. Benditt, Proc. natn. Acad. Sci. U.S.A. 73, 3723 (1976)]. The present study more fully characterizes the mono-oxygenase activity in aortas of treated and untreated New Zealand White rabbits. A 2-fold activation was obtained with NADH (7 × 10-4 M) at saturating concentrations of NADPH. Addition of heme (9 μm) increased the enzymatic activity 2- to 4-fold during a 15-min incubation and over 25-fold during a 2-hr incubation. The results suggest the presence of relatively high concentrations of apoprotein in the aortic tissues. Kinetic studies in the presence of heme yielded an apparent Km of 1 × 10-4 M and Vmax of 15.24 pmoles/mg of protein/min with respect to NADPH. A sigmoidal curve was obtained with varying benzo[a]pyrene concentrations (0.5 to 80 μM), suggesting the possibility of allosterism. Aroclor 1254,3-methylcholanthrene and 5,6-benzoflavone acted to induce the cytochrome P-450-dependent mono-oxygenase, while pheno-barbital and pregnenolone 16α-carbonitrile demonstrated little, if any, induction capacity. Analyses of metabolites formed in induced aortas with high-pressure liquid chromatography revealed the formation (in each case) of primarily the phenolic metabolites of benzo[a]pyrene.
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U2 - 10.1016/0006-2952(79)90520-3
DO - 10.1016/0006-2952(79)90520-3
M3 - Article
C2 - 34402
AN - SCOPUS:0018377857
SN - 0006-2952
VL - 28
SP - 305
EP - 311
JO - Biochemical Pharmacology
JF - Biochemical Pharmacology
IS - 2
ER -