Direct effects of intermediate metabolites of 37 different xenobiotics on the catalytic activities of both reconstituted cytochrome P-450IIB1 and P-450IA1 enzyme systems were studied by determination of NADPH oxidatio...Direct effects of intermediate metabolites of 37 different xenobiotics on the catalytic activities of both reconstituted cytochrome P-450IIB1 and P-450IA1 enzyme systems were studied by determination of NADPH oxidation at various intervals after initiation of the reaction. The results showed that cytochrome P-450IIB1 isozyme was much more likely than cytochrome P-450IA1 isozyme to be attacked by the reactive intermediates formed by some xenobiotics with smaller molecular weight and lose its catalytic activities. These xenobiotics were carbon tetrachloride, chloroform, carbon disulfide, benzene, parathion, methylparathion, methyldursban and dimethylnitrosamine. In contrast, however, steadily increasing metabolic activities were observed towards benzo(a)pyrene, 3-methyl-cholanthrene and polychlorinated biphenyls in reconstituted cytochrome P-450IA1 enzyme system as the reaction time prolonged within 4 min. The method discussed in this paper could be used as a simple and convenient way to observe directly the autocatalytic destruction of P-450 enzymes by some chemical agents.展开更多
The evaluation of luminol-dependent chemiluminescence (CL) for determination of free radicals generated during the oxidative reactions of microsomal enzymes in microsomes and reconstituted systems has been studied. Th...The evaluation of luminol-dependent chemiluminescence (CL) for determination of free radicals generated during the oxidative reactions of microsomal enzymes in microsomes and reconstituted systems has been studied. The results indicated that the CL not only depended on NADPH induction but also on intact cytochrome P-450 enzymes. The light emission signal was strongly scavenged by SOD with inhibition rate of 93 %. A concentration of 24 /μmol.L-1 cadmium acetate and 2.5 μmol.L-1 mercuric chloride also inhibited the signal significantly as compared with the control. The study of CL in detecting free radicals formed by biotransformation of 44 xenobiotics suggested that some of the compounds known as free radicals producing agents by bioactivation increased the light emission in cytochrome P-450 enzyme system, such as carbon tetrachlonde, chloroform, tetrachloroethylene etc., the others forming toxic metabolites by biotransformation induced the CL in some cases, such as carbon disulfide, benzene, methyldursban, methylparathion etc. or decreased the light emission, such as parathion, aniline and polychlorinated byphenyls etc., and still others whose toxic effects have no relationship with their biotransformation had no influence or an inhibitory effect on the CL, such as aminopyrine, TOCP, and acrylamide. CL in the cytochrome P-450 enzyme system remained unchanged during the biotransformation of carcinogens such as diethylnitrosamine, dipropymitrosamine and benzo (a) pyrene as compared with the control. However, 3-methylcholanthrene and dimethyInitrosamine had an enhancing effect on the CL, while 2-acetylaminofluorene and 2-aminoanthracene showed an inhibition to the signals.展开更多
文摘Direct effects of intermediate metabolites of 37 different xenobiotics on the catalytic activities of both reconstituted cytochrome P-450IIB1 and P-450IA1 enzyme systems were studied by determination of NADPH oxidation at various intervals after initiation of the reaction. The results showed that cytochrome P-450IIB1 isozyme was much more likely than cytochrome P-450IA1 isozyme to be attacked by the reactive intermediates formed by some xenobiotics with smaller molecular weight and lose its catalytic activities. These xenobiotics were carbon tetrachloride, chloroform, carbon disulfide, benzene, parathion, methylparathion, methyldursban and dimethylnitrosamine. In contrast, however, steadily increasing metabolic activities were observed towards benzo(a)pyrene, 3-methyl-cholanthrene and polychlorinated biphenyls in reconstituted cytochrome P-450IA1 enzyme system as the reaction time prolonged within 4 min. The method discussed in this paper could be used as a simple and convenient way to observe directly the autocatalytic destruction of P-450 enzymes by some chemical agents.
文摘The evaluation of luminol-dependent chemiluminescence (CL) for determination of free radicals generated during the oxidative reactions of microsomal enzymes in microsomes and reconstituted systems has been studied. The results indicated that the CL not only depended on NADPH induction but also on intact cytochrome P-450 enzymes. The light emission signal was strongly scavenged by SOD with inhibition rate of 93 %. A concentration of 24 /μmol.L-1 cadmium acetate and 2.5 μmol.L-1 mercuric chloride also inhibited the signal significantly as compared with the control. The study of CL in detecting free radicals formed by biotransformation of 44 xenobiotics suggested that some of the compounds known as free radicals producing agents by bioactivation increased the light emission in cytochrome P-450 enzyme system, such as carbon tetrachlonde, chloroform, tetrachloroethylene etc., the others forming toxic metabolites by biotransformation induced the CL in some cases, such as carbon disulfide, benzene, methyldursban, methylparathion etc. or decreased the light emission, such as parathion, aniline and polychlorinated byphenyls etc., and still others whose toxic effects have no relationship with their biotransformation had no influence or an inhibitory effect on the CL, such as aminopyrine, TOCP, and acrylamide. CL in the cytochrome P-450 enzyme system remained unchanged during the biotransformation of carcinogens such as diethylnitrosamine, dipropymitrosamine and benzo (a) pyrene as compared with the control. However, 3-methylcholanthrene and dimethyInitrosamine had an enhancing effect on the CL, while 2-acetylaminofluorene and 2-aminoanthracene showed an inhibition to the signals.
